One of the best things about Recreational Vehicles (RVs) is that they are designed to be used with or without power, water, and sewer hookups. This is mostly possible because of RV ‘house’ batteries that power interior lights, water pumps, and vent fans. RV Batteries can also power 110V/120V electronics like your TV if your RV has a power inverter.

Unfortunately even the best batteries don’t last forever and most RV manufacturers do not install the best batteries. Add to this that many RV manufacturers use cheap single-stage Battery Converter Chargers that damage batteries over time, and most RV owners find their first set of batteries dead (or close to it) after their first year of RV ownership.

In this article I’ll explain in layman’s terms how to get the most power for the least cost from your RV house batteries, what types of batteries are available, and how RV batteries work. I’ll also show you our battery setup and explain why I chose Trojan T-105 6V Golf Cart Batteries charged by an IOTA-DLS45 4-Stage Smart Converter.

I’ll cover the basics, which is still quite a lot of information, and hopefully this article helps you find the right battery and converter setup for your RV.

If you’d like a deeper understanding of batteries, check out Battery University.  This free site is dedicated to teaching people everything (and I mean EVERYTHING) there is to know about batteries. I link to their info throughout below, but only for those who want to know more (like me). For everyone else who just needs an overview – read on →


Single Stage RV Battery Charger/Converter

I’m going to start this article about RV batteries by first addressing the cause of most RV battery problems – the single-stage battery charger/converter. If your RV has house batteries then it also has a charger/converter. If you have a nicer or newer RV, then you may already have a ‘smart’ charger, or 4-stage charger. If that’s the case feel free to skip this section.

Our Old Single Stage Converter
Our Old Single Stage Converter – Only Good for Killing Batteries and making a lot of fan noise!

Most RVs include a converter / charger – a device that turns 120-volt A/C power into 12-volt DC power while also charging the RV house batteries. The converter powers your 12-volt appliances such as lights, vent fans, your TV antenna, water pump, electric awnings, etc.. when your RV is plugged in to shore power or running off your generator. You might be thinking, “Wait a minute, I thought my batteries did all of that?” But in fact, when you’re plugged into shore power, you can literally remove your RV house batteries and all you 12-volt appliances will still work just fine.

The converter also sends some of that 12-volt power to the batteries to charge them – which is why Converters are also called Battery Chargers – or Converter/Chargers.

The problem is that many factory-installed converters use just one consistent voltage – usually 13.6V to 13.8V to charge and maintain RV house batteries. This is why they’re called ‘single stage’ converter/chargers. This is a problem because batteries charge faster, last longer, and function better when charged by a 4 stage ‘smart charger’. The four stages – which I’ll cover below – are bulk (14.4V – 14.8V), absorption (13.8V – 14.2V), float (13.2), and then periodic equalization charge (15.5V) to ensure no battery sulfation  (a poor or reduced battery charge)  takes place.

When you maintain batteries at 13.7V they take forever to charge on the front end if they fully charge at all, and then they get cooked once the battery is charged. And when I say cooked, I’m not kidding. the charger literally boils some water out of the batteries, which speeds up the sulfation process and the batteries require more frequent maintenance – or they die much faster than they otherwise would.

By starting with a heavy bulk charge, and then switching to an absorption charge when the battery is ~80% full and a float/trickle charge at 95% full, your house batteries will reach 100% capacity without risk of sulfation or outgassing. They’ll also charge much faster – especially the first 80% – and last much longer.

Finally, keeping the batteries at a 13.2V float charge keeps them cooler and they require less maintenance (water & terminal cleaning) as a result. This also prevents excessive sulfation, which is the death of any lead acid battery.


Battery Charger/Converters & RV Generators Issue

Another issue that a lot of RVers run into is trying to charge their batteries by running the generator. If you have a smart charger (below), then you can get a pretty good charge (85%) in a couple hours.

If your RV is equipped with a single-stage converters (like ours was), then trying to charge your batteries by running the generator is expensive and mostly pointless. Charging the batteries from 50% discharge at a consistent 13.7 Volts takes much longer without the higher voltage bulk (14.8V) and absorption (14.2V) stages that a smart converter provides.

If you plan to boondock and charge your batteries with your RV generator then upgrading to a smart converter charger is a must.


The Solution: The 4-Stage Smart Battery Charger / Converter

IOTA-DLS45 Smart Converter

Right after upgrading our batteries I replaced our single stage converter with an IOTA-DLS45 4-Stage Smart Converter/Charger.

As newby RVers we were told we’d need to buy a new set of house batteries every year on average. I’ve also read on forums that house batteries only last 1 – 2 years, and that’s ‘just the way it is.’

The truth is, this problem is mostly due to the low-quality single-stage battery charger/converters that are installed in most RVs (and junk batteries installed in some).

With a proper 4-stage smart converter/battery charger like our IOTA, our Trojan T105 batteries should last 7 – 10 years. I’ve heard of Trojan batteries lasting even longer in some case, as battery life varies some based on use, care, and number of charge cycles.

A new set of batteries costs $200+, so by only replacing them every decade vs. every year or two, we save hundreds of dollars. Not only that but our batteries actually work as designed, and we don’t have to worry about running out of power. Imagine using lights and watching a movie before going to bed without worrying if the propane heater blower will have enough juice to run all night, or if the toilet will flush in the morning (since the water pump runs on house batteries).

That’s standard for us now that I’ve installed our Iota Smart Charger Converter and Trojan T-105 Batteries. Meanwhile, I read about people struggling with undercharged or half-dead batteries every day.

If your batteries have been chronically undercharged or abused by a single-stage converter, they may need to be replaced. That said, I recommend upgrading the charger converter first, and then replace the batteries if they aren’t holding a charge from your new smart charger converter.


Which Smart Charger Converter Should You Get?

Both Iota and Progressive Dynamics make excellent smart battery charger converters and it’s a matter of preference between the two. The IOTA units are a little less money and a slightly smaller footprint, so that’s why I chose the IOTA DLS45.

The easiest way to get the ‘right’ smart charger is to match the amperage of your current battery charger converter. Some people get confused and try to match the line amperage (30amp or 50amp) of their RV, but these are measuring two different things. Your RV plug is 110V, the charger converter is 12V. That’s why our 30-amp RV has a 45-amp charger converter.

I’ve linked to a few of the more popular smart chargers below. The first link is the IOTA we use, and it’s worked exactly as designed for several years now. RVs larger than ours likely use the 55 amp model instead.

IOTA-DLS 45amp 4-Stage Smart Converter/Charger on Amazon.com →

IOTA-DLS 55amp 4-Stage Smart Converter Charger on Amazon.com →


Battery Amp Hours explained

Before I get into battery types, I think it’s helpful to go over battery amp hours. Amp Hours are the most useful and most common way to measure RV battery storage capacity. I think it’s easiest to think of Amp Hours (AH) as units of electricity in a battery ‘gas tank’ of sorts.

Simply put, 1 amp hour (1AH) is the amount of power it takes to run a 1 amp electrical draw for 1 hour. So, for example: An LED lightbulb may use 0.5 AH. If you run 1 LED light for 6 hours, you’ll use 3 Amp Hours (1 x 0.5 x 6 = 3). If instead you run 6 LED lightbulbs for 1 hour, you’ll also use 3 Amp Hours (6 x 1 x .5 = 3). If you have 100AH of available charge in your RV batteries then you could run those 6 lights for just over 33 hours before you empty the batteries ‘tank’ (6 x 33.3 x .5 = 100). Make sense?

Amp Hours are usually measured using the ’20-hour rate.’ What that means is that if you used all the power that a battery can hold over a 20-hour period, then you would have used X amount of amp hours, with X being the Amp Hours at the 20 hour rate.

Why the 20-hour distinction? This is because batteries supply more total Amp Hours when their power is used very slowly, and they supply less Amp Hours when the power is used quickly (high draw). That ironically means that people who use the most power actually get the least amount of total power from their batteries.

The most important thing about the 20-hour rate is that it gives you good comparative data between batteries. Our Trojan T-105s have 225AH of capacity at 20 hours. I can compare that to other batteries and then know what to expect if I switch or upgrade.

If the battery I’m comparing it with has a wonky rating – like a 1-hour rate, then it’s next to impossible to compare the batteries. Be careful of any battery that doesn’t come with a 20-hour Amp Hour rating, as some cheap batteries will try to trick you with weird measurements.


The Most Common types of RV House Batteries

Once you have a decent smart converter/charger, either your current batteries will begin to hold a charge – or they won’t. If they don’t then no big surprise as you’re probably reading this article because your batteries died in the first place. It was still very much worth it to upgrade to a smart converter so that your next set of batteries won’t suffer the same fate as your last set.

I studied RV Batteries pretty extensively before buying our new set as I wanted to make sure I got the best batteries for the money and for our lifestyle. This is important, because if you spend 100% of your time plugged into shore power, batteries are a lot less important than if you boondock regularly (stay overnight with no hookups).


12-Volt RV/Marine Flooded Cell Lead Acid Batteries

12V RV/Marine Battery
12V RV/Marine Battery

These are the most common batteries installed in RVs. While these are called ‘deep cycle’ batteries, they’re really a hybrid starter/deep cycle.

The difference may sound like marketing, but in real world use a true ‘deep cycle’ battery can be more deeply discharged and bounce back than a hybrid starter/deep cycle battery. Deep cycle batteries also last longer, and usually hold more charge, too.

If you’re on full hookups most of the time, then an inexpensive set of 12-Volt RV/Marine batteries are a good choice. They usually cost less than $100 each and can be bought at Walmart and most auto-parts stores. These batteries will still benefit by the use of a 4-stage smart charger, as they’ll last significantly longer and provide more power.


6-Volt Deep Cycle Batteries aka Golf Cart Batteries

Trojan T105 Golf Cart Batteries

By definition, a deep cycle battery can be discharged 80% of it’s maximum charge, and then can still be fully recharged without damaging the battery. Don’t try that with RV/Marine hybrid batteries!

6-Volt Deep Cycle Batteries are designed for and used in golf carts. In other words, they’re workhorses that are designed for abuse and they last a long time.

If you full-time or most-time and spend a fair bit of your time traveling, boondocking, and off-hookups, then these are the batteries I recommend.

Our Trojan T105 Batteries are 6V Golf Cart batteries, which I bought, and then wired in series, essentially creating 1 big 12-volt battery. Note that to use 6V batteries you must have an even number of batteries. You can’t wire 3 or 5 of these together and get the necessary 12-Volts.


12-Volt or 6-Volt AGM Batteries

Lifeline AGM Batteries
Lifeline AGM Batteries are the industry standard

In regular lead-acid battery cells, the acid is in liquid form – which is why they’re called ‘flooded cell’ batteries. In VRLA (valve regulate lead acid) batteries such as AGM, the acid electrolyte solution is immobilized, either by soaking a fiberglass mat in it (hence: Absorbed Glass-Mat batteries), or by turning the liquid into a paste-like gel by the addition of silica and other gelling agents (hence: gel batteries).

The net result of this is part good and part bad.

The good is that AGM batteries hold a charge much better than traditional flooded cell batteries. If you store your RV for months at a time, then I recommend AGM batteries, since their rate of resting discharge is tiny compared to flooded cell batteries (either 12-V or 6-volt).

That means you can leave the batteries in your RV between trips without having to worry about keeping them charged. I’d still remove them and trickle charge them in the winter, but even there they’ll only need to be charged every few months – vs. every week or two for flooded lead acid.

The bad is that AGM batteries cost roughly double what traditional flooded cell batteries. A comparable AGM also weighs more than a flooded cell battery – in both cases assuming similar Amp-Hour capacity.

Lastly, it’s not possible to open, inspect, or fill AGM batteries. This means they won’t last as long as well-cared for flooded cell batteries – which is because AGM batteries still outgas. That’s why they’re called ‘Valve Regulated Lead Acid’ batteries. They have a valve that allows outgassing when pressure builds up in the battery due to overcharging or rapid discharge (electrolysis). The vapor that’s vented can’t be replaced since the batteries are sealed.


Lithium (LiFePO4) Batteries

We don’t have Lithium batteries so I can’t speak to their real world use. Lithium Iron Phosphate batteries offer many features that make them a good choice over lead acid batteries, such as faster charging, more capacity per size/weight, more consistent power discharge, deeper depth of discharge, and more recharge cycles (longevity).

Unfortunately Lithium batteries are also almost 10-times more expensive than comparable lead acid batteries – or 5-times more expensive than AGM batteries, so unless you boondock a lot and rely on Solar Power Lithium batteries, they are not a practical or affordable option for most RVers.

If you’d like to know more about lithium batteries for RVers, I recommend reading the Technomads Lithium Battery Page.


What Batteries are Right For Your RV?

AGM Batteries are the best option for most RVers. I say this largely because most RVers part time, and most people don’t need another maintenance item (gotta fill/charge the RV batteries) in their brain space.

For full-timers, boondockers, and those who like to keep an eye on and maintain things – and those who want the best bang for their buck – 6-Volt flooded cell (Golf Cart) batteries are the way to go.

If you never leave the RV park, stick with inexpensive 12V RV/Marine batteries. If you never leave the RV park, then you really only need one as a backup if the power goes out.


Our Battery Setup

I’d known that our batteries weren’t holding much charge for a while, but it took a storm in Blaine, WA that knocked down power lines for us to make a battery upgrade a priority. The first night after the storm while running on 100% battery power our lights were dim by 9pm and our vent fans were useless – not good!

We also had an RV trip to Mt Lassen Volcanic National Park planned, and knew we’d be off hookups for several days. New batteries were a must.

On the plus side, I’d been planning to upgrade our batteries for some time, as we’d made a goal to do more boondocking (camping outside of developed campgrounds, so no hookups). We’d also like to spend more time in State & National Parks and other off-grid camping.

Our RV came from the factory with two NAPA 12-Volt RV/Marine ‘Deep Cycle’ batteries. These are commonly installed in RVs as they’re relatively inexpensive and they’ll do the job – at least for a year or two. Unfortunately these are cheapy hybrid starter batteries that aren’t designed for deep cycling.

Our house batteries are installed under our entrance step in a ventilated compartment. There’s only room for two batteries, but considering the size of our RV and our power requirements, two batteries is plenty for us.

How to wire batteries in Series vs in Parallel

I measured the space, determined I could fit two Trojan T-105 Batteries, then I went to Battery Systems of Bend, OR, and picked up two fresh Trojans. A good battery shop is your best bet for new batteries, as in many cases they can’t be shipped, and shipping something as heavy as a battery is very expensive.

It’s important to wire 6V batteries correctly. I’ve included this diagram (that I made) to illustrated the right way to wire 6V batteries vs. 12V batteries.

To ensure that our new Trojan batteries will last, I ordered the DLS-45 IOTA Smart Charger and installed it in place or our single-stage converter charger. I didn’t document this unfortunately – although every setup is different, so not sure that would have helped much.


How Lead Acid Batteries Work

Lead Acid Batteries

The vast majority of RVs use some type of lead-acid battery. This includes both flooded cell (most common) and AGM (Absorbed Glass Mat – also common) batteries. Even your engine starter batteries are a type of sealed lead-acid battery.

In conventional lead-acid cells, the diluted acid is in liquid form, hence the term “flooded” or “wet” cells. AGM batteries have the same lead-acid chemistry, but the acid electrolyte solution is immobilized, either by soaking a fiberglass mat in it (hence: absorbed-glass-mat batteries), or by turning the liquid into a paste-like gel by the addition of silica and other gelling agents (gel-cell batteries).

Lead acid batteries contain 2 lead plates (electrodes) suspended in sulphuric acid (electrolyte). To be fully accurate the negative plate is lead and the positive plate is lead dioxide. When you pull power from the battery (discharge), the lead and acid in the battery undergo a chemical reaction that produces lead sulphate and water.

When the battery is recharged, or has current run through it, the lead sulphate and water are turned back into lead, lead dioxide, and acid. When the battery is back to 100% lead, lead dioxide, and sulfuric acid, then the battery is full charged.

For the full chemical reactions, read this wikipedia article


How to Damage or Ruin RV House Batteries:

RV House Batteries are designed to be discharged and recharged many hundreds of times, however there are 3 things you can do that will kill your batteries well before their time:

Fully Discharge The Battery – If batteries are fully discharged – even once – they will no longer hold a charge. Sometimes batteries are only mostly dead, and in those cases it may be possible to bring them back to life gradually with a trickle charger. In general if a lead acid battery reads 10.5-volts on a voltmeter, it’s permanently dead and you’ll need to replace it.

Not Charged Fully, or not Charged Often Enough – As batteries are discharged the lead and acid reaction forms sulphate. Sulphate starts as a sludge that is easily turned back into lead, lead dioxide, and acid when the battery is charged. If the battery stays in a discharged state for too long (a couple weeks+) the sulphate slowly hardens and crystalizes on the positive and negative plates. This reduces battery capacity in the short term and kills the batteries over time. This is the #1 cause of RV battery premature death, as most RVs have lousy battery charger converters or don’t maintain their batteries properly.

Letting Batteries Dry Out – The other easy way to kill a set of lead acid batteries is by not adding water. Lead Acid batteries have vents so that they won’t explode during outgassing (electrolysis). Outgassing can happen either due to excessive discharge (high-draw 12V battery usage) or overcharging with a bad converter/charger. Lead acid batteries have vents to release excess gases and water vapor from outgassing, but the lost water needs to be replaced. The lead plates must be submerged to function – exposing the plates to air will kill your batteries quickly.


How to Maintain RV Batteries:

Batteries are at their best when they have clean terminals, are fully charged, and full of acid. That means they should always be stored fully charged and full. That also means they should never be stored partially charged, or not full of water/acid.

That’s because the enemy of your battery life is sulfation. This is caused by lead sulfate – which is only present when your batteries aren’t full charged. Lead sulfate hardens on the battery plates and then doesn’t go back into solution, so it ruins your batteries two ways. Keep your batteries charged and this won’t be an issue.

If you have AGM batteries, then the only maintenance you’ll be doing is charging the batteries and keeping the terminals clean.

For flooded lead-acid batteries -including golf cart batteries – regular charging and occasional watering are necessary.

How To Clean Battery Terminals

Cleaning battery terminals is easy if you have the right tools. A terminal cleaning brush, a ratchet set, and some vaseline (optional) are all you need.

First – what is the stuff that forms on your battery terminals? The positive and negative terminals each tend to form their own powdery residue – but you’re more likely to see blue/green residue on the positive terminal and white on the negative.

The greenish blue stuff is copper sulfate that usually gets a little caked up as it’s exposed to moisture. Copper sulfate is made by a reaction between the copper terminal clamp and the lead in the battery, plus some outgassing from the sulfuric acid in the battery. Copper sulfate is not good at conducting electricity, so you need to periodically remove it. A thin layer of vaseline is a good way to prevent it from reforming.

A lot of people are scared to touch battery terminals – and rightly so. Getting an electrical shock is not fun. For best results always disconnect the negative battery terminal first. Make sure the terminal clamp is not touching the terminal. Then disconnect the positive battery terminal. Once disconnected, you can clean the battery terminals without worry – as long as you don’t touch both positive and negative at the same time and complete the circuit.

If you don’t have a battery terminal cleaning brush then you can use any small wire brush to clean your battery terminals. That said, a battery terminal brush makes the job easy and is recommended.

Battery Terminal Cleaning Brush on Amazon →


How to Add Water to RV House Batteries

Adding water to your RV’s house batteries is very easy. You’ll need distilled water and battery syringe filler and about 5 minutes. House batteries have either 3 (6V) or 6 (12V) cells to fill each. To fill battery cells simply unscrew the vent cap. This can be done either by hand or sometimes with a screwdriver.

Important – ONLY use distilled water when adding water to batteries. Distilled water has no electrolytes (salt), so nothing that can react with the acid and lead plates in the battery. Distilled water is sold in the water section at most stores.

Battery cells should typically be filled up to 1/8-inch below the lip. There’s no need to measure, just fill until it’s just below the visible lip. Then close that cell and move on to the next one. Make sure you fill every cell in every battery – and that’s it.

To ensure that you get the water into the battery, use a battery filler. It looks like a big turkey baster. Squeeze the bulb, stick the tube in your gallon of distilled water, fill the bulb, then transfer the water to a battery cell until it’s full.

Battery Filler Bulb on Amazon.com →


Wrapping Up

This is a relatively shallow dive into a large subject. I didn’t cover everything by a long shot, so if you have questions please leave them in the comments and I’ll answer or add to this article.

This page could also use a glossary, as there are many battery terms listed above that don’t include a definition or explanation. I’ll add this as necessary, so again – let me know if you have any questions.

Beyond that, I hope you find this article helpful the next time you think about shopping for RV house batteries!

Author

Hi, I'm Rich - Perpetual traveler, photographer, writer, and web designer. Thanks for reading, and happy trekking!

81 Comments

  1. Rich, I have heard that its best to replace both 6v batteries at the same time even if one is still good. Does that sound right?

    • Yep, that’s correct. When you wire batteries together you’re essentially making one big battery that is constantly trying to equalize the charge across all cells. If half of the cells are old or degraded (old battery), then it will impact the new battery and age it much more quickly. You’ll get the best life out of your batteries if you use 2 news ones.

  2. Thank you for the information. My 12V batteries have died and I am looking to replace/upgrade I have a 2017 travel trailer Rockwood Roo. I was given the following information:

    I have been researching your 4 stage charger and found that the 4 stage charger is not needed on AGM batteries. It is a needless expense. 2 of the 4 functions are not used on AGM’s.
    1. 2000 watt inverter / charger. This will be discounted somewhat but I do not know how much. $1099.00 + $59.00 INSTALL.
    2. 2 heavy duty AGM 6volt batteries. 255.49 each Install $85.68 total
    3. Additional wiring needed. $270.00
    4. Supplies 125.00
    Total $2,149.66 plus tax.

    Would appreciate your thoughts on this recommendation.
    Thanks, Melissa

    • Rich Reply

      Hi Melissa – you’re right that AGM batteries are less prone to sulfation and therefore don’t need the equalization charge as often – but they still will sulfate over time and do benefit from equalization. Also, a smart charger is designed to charge your batteries correctly and without overheating them and causing outgassing. And Yes, AGMs can overheat and do vent, which causes a small permanent loss of capacity each time. RV Batteries are also sensitive to temperature, and should be charged at the correct voltage for whatever temp. Most are exposed to the outside, so it can make a pretty big difference. A smart charger will charge at the correct voltage vs. a fixed voltage charge will not. For more information, read this for details: https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

      As far as your install, that sounds a little pricy on the inverter/charger to me. You mention that it will be discounted, but didn’t mention the brand. The brand matters.. The price of everything else looks ok – but again,, the brand of the AGM batteries matters a lot. Do some research on battery brands. The better brands – Trojan, Crown, Lifeline, etc.. are worth the extra price as they’re more useable and will last longer. Is the additional wiring for wires from the inverter to outlets throughout the RV? Sounds pretty reasonable – I’d be curious if there’s install cost for that as well.

      • Thank you Rich
        I’m trying to make a decision on what we need as opposed to what I’m being sold. I will double check brands.
        Is a 2000watt inverter/charger necessary? Installing another breaker? Rewiring the trailer? What benefits are there from installing this?? Using a microwave??
        We only use the batteries to charge electronics, run a CPAP at night and maybe a movie on the TV, water pump
        water heater, fridge and heat are propane
        Sorry, this decision just makes me go in circles. I don’t truly understand it, no matter how much I read through.

        What are your thoughts on Lithium 12V batteries? $$$ but worth the investment?
        Thank you

        • Rich Reply

          Hi Melissa – Even with a 2K Watt inverter you’re pushing it to use a Microwave (1800K Watt). You really don’t want to use batteries to run things that max out power draw, as that’s when batteries get hot and (potentially) lose capacity.

          For me to tell you all the benefits, I’d need to know how your trailer is currently wired. Do you currently have an inverter? If so, how big is it? If you’re only running a CPAP at night and watching a movie, it certainly doesn’t require Lithium batteries (very pricey).

          How long are you typically off grid? (not plugged in) If you’re only camping for a weekend at a time – overnight or maybe 2 nights, then your requirements are different than if you camp for a week off grid. If you’re plugged in most of the time when you camp, your requirements are different as well. Any info you can give me helps my reply. Thanks!

  3. I have 2 100 watt solar panels with 2-12V battery’s. I’ve never changed the inverter/charger so I assume it’s a single stage. I rarely if ever plug in since the solar takes care of things. Recently on an October trip near Bishop Ca, the temps dropped into the 20’s and we lost battery power due to running the heater more than normal. I figured I would need new battery’s since mine are 4 years old now. Do you think it’s still important to buy a multi-stage converter? Since I never plug in wouldn’t the solar controller regulate the battery and know when to slow the charge down as it reaches full charge? I got 4 years out of cheap 12 volt battery’s using this set up with cheap 12v battery’s.

    • Rich Reply

      Hi Dana – You’re correct, your solar charge controller charges the batteries and (hopefully) keeps them topped off. In your configuration a 4-stage converter/charger isn’t as necessary.. and if you’re getting 4 years out of inexpensive 12-Volt Batteries, then I’d say if it isn’t broke.. – Good luck!

    • Thanks for the great write up. I went with your recommendation and bought the two t-105s and and the Iota dls-45. When I assembled everything I heard the batteries making a bubbling noise and that got me doing some research. I found some recommendations of supplying the batteries with 10% the 20hr amps. So a 225 system would be best charged by a 22.5 amp charger?
      Being that the batteries are in series they stay 225 amp hours at the 20 hour rating right? And the iota dls is rated at 45 amps for bulk charge? That would be 20% the 20 hour rating. Any insight on this or some information to put my mind at ease would be great. The voltage is perfect but just curious about the amps. I don’t want to overcharge my two new batteries:) thanks for all the great info.

      • Rich Reply

        Hi Scott – The amperage of the IOTA doesn’t make a huge difference. Charging the batteries is more about voltage. It’s similar to your car alternator – it needs extra capacity to power your 12V appliances while also charging your batteries. The IOTA is charging your batteries at the same time as it’s powering lights, running fans, your furnace blower, etc.. That said, it shouldn’t be boiling the batteries. Is the bubbling noise loud?

        First, make sure you have the batteries properly wired in series. You should have the batteries connected from a negative on one to a positive on the other – that’s it. Second, make sure the batteries have enough water. They should be filled with distilled water to just below the feeder tube (1/8″ below). Next – do you have a volt-meter? Check and see how much voltage the batteries are taking in. On bulk it should be 14.6 – 14.8, absorption 13.9 – 14.1, then float around 13.1 – 13.2 (depends on temp). It’s also possible the IOTA is giving the batteries an equalization charge, which is over 15V. That’s part of what the smart charger does, but it shouldn’t stay that high for very long. If you’re seeing different voltages, then the IOTA may be a bad unit. And yes, wired in series they stay at 225amp hours.

        The other reason you want a 45amp unit is because that’s the most power the unit can add to the batteries in an hour (there’s always some loss). If you’re boondocking and recharging with the generator it will take twice as long to add power to the batteries with a 22.5amp unit – or longer if you’re using lights/fans/etc.. The 45amp unit is much faster/better. I’ve never had an issue with this setup and I’ve been using it for years – plus the single stage charge/converter unit that came in our RV was rated at 45amps too. I hope that’s helpful – good luck!

        • Does the amperage of the IOTA need to match the service to your RV? For example, my TT plugs into a 30AMP outlet, does that mean I need to buy a 30AMP charger/converter?

          • Rich

            Hi Mark – no, those are two different things. Your 30AMP Outlet is 110/120V power in, whereas the IOTA unit is taking some of that 110/120V power and turning it into 12V power (that’s the ‘converter’ part of charger/converter). The IOTA needs to have enough capacity to run your 12V appliances while you’re plugged in (vent fans, furnace blower, lights) and also charge and condition your batteries at the same time. It’s pretty common for a 30AMP rig like yours to have a 45AMP Converter Charger. That’s how our rig was configured.

  4. I am running 4 6 volt golf cart batteries (2 in series to get 12 volts and then each series wired parallel) and have a question about how and where to connect house cables and inverter. It seems if I connect all the cables on the same series I would be using that series only and just balance charging it with the other series. Does that make sense or am I just making this too difficult – does it matter at all?

    • Rich Reply

      Hi James – I follow you. Yes it matters! You should have 2 sets of 6-volt batteries wired in parallel – This creates 2 double-capacity 6-volt batteries. At this point think of them as one battery each. Next you connect those batteries in series by connecting a negative on Battery Bank 1 (BB1) to a positive on Battery Bank 2 (BB2). You then need to connect the positive from the RV to a positive on BB1 and the negative from the RV to a negative on BB2. That gives you: RV+ +BB1- +BB2- -RV (just like putting two batteries in a flashlight).

      Technically you can connect RV+ to either battery in BB1 because they’re wired together in parallel so essentially just one big battery (same on the other end with BB2). It’s still preferable to wire it to the battery that isn’t connected to the other battery bank in series. That forces the power to go through all 4 batteries equally and yields the best results over time.

      If this is still confusing, then check out this page on battery configurations: https://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html – it shows your exact configuration toward the bottom of the article.

  5. PEEWEE HENSON Reply

    WE KNOW ABOUT BUDGETS. BEFORE WE RETIRED THE MOST I’VE ASKED OF MY SINGLE 12 VOLT DEEP CYCLE WAS “PLEASE LAST THE ENTIRE NIGHT”. NOW, WHEN WE HEAD OUT ITS MULTI NIGHT TRIPS. I SHOT WHAT LITTLE WAD I HAD AND BOUGHT 2 6VOLT GOLF CART BATTERIES (duracells, trojans were beyond budget friendly). FULLY CHARGED WHEN WE LEAVE THE HOUSE AND 3 NIGHTS OUT. BATTERIES NEVER FELL BELOW 11.9 VOLTS ON THE METER. AND WE HAD THE HEATER ON EVERY NIGHT. HAPPY WIFE=HAPPY LIFE

  6. Tank you so much for your write up!
    Just wondering what your thoughts are on the Trojan T145 battery. I installed 2 of them in our last motorhome and they worked great for 9 years and we boon dock quite a bit. The few more amp hours are worth it to us for the peace of mind while boon docking.
    A few months ago we traded in our motorhome for a brand new 2018 model. It has a full size residential fridge that runs off of an inverter so we have a bank of four 6V batteries. On our first boon docking trip in it, the batteries discharged badly over the trip, especially over night. One morning we woke up to the house batteries at 10.5 volts so the next day we charged the hell out of them running the generator most of the day. The next morning we woke up to the batteries at 6.8 volts. This combined with the fact that I just found out from the manufacturer of the motorhome that it was on the lot for 15 months before we bought it and I know they didn’t maintain the batteries in that time. Hopefully, I can get the dealer to cover some of the costs, but I will be installing 4 new T145s soon.
    Your write up on the smart converter makes a lot of sense and I think I’ll look into installing one in our new rig.
    Thanks again,
    Mark

    • Rich Reply

      Hi Mark – the T145s are great batteries too. In our case we didn’t need the extra capacity – and the T145s weigh more, and cost more – plus as they have higher capacity it takes longer to charge them. All that said – they sound like a good fit for your situation.

      Residential fridges are getting increasing popular for obvious reasons, but they’re not boondocking friendly as you’ve found out. It’s helpful to do the math – I’ve read that in a 24 hour period, a residential fridge uses around 400 amp-hours(!) of converted 12V power (requires inverter) so they use a ton of power if you’re pulling from batteries.

      If you have 4x Trojan T145, you’ll have 520amps of total capacity, but you should only regularly drain the batteries half way – so you’ll have 260 amps of useable capacity. That’s not enough to cover the 400amps the Fridge requires daily – let alone your other 12V usage (water pump, lights, vent fans). That means that unless you have solar power you’ll need to run the generator for a couple hours in the morning, and again for a couple hours in the evening to keep the batteries charged enough to run the fridge overnight.

      It sounds like you’re ok with that solution – and yes, using a 4-stage charger/converter is a must if your RV doesn’t already have one. Adding some solar panels would go a long way too and would likely save you from running the generator in the evening (saves some gas). Good luck!

  7. I just recently purchased a class 8 conversion . It had two large Napa commercial 8D 12v batteries as the house batteries.The weird thing is that they were wired in series which doesn’t make sense to me. There is no inverter installed any where that I can find. There is a solor system that I am still trying to understand. And there was a charging wire coming from one of the trucks alternators. Both batteries are bad so I was thinking of using 4 6v deep cycle (golf cart style) batteries wired in series/ parallel to get my 12v and a large reserve capacity. And I will add a 4 stage converter. My current TT has a converter and alternator wire but no solor, any harm in having the three sources for charging?

    • Rich Reply

      Hi Adam – some RVs run on 24V instead of 12V. It sounds like that may be the case with your Class B8 conversion. Double check, because lights, fans, blowers etc.. will all require 24V and you don’t want to wire in 12V unless you’re going to replace everything.

      Regarding Solar – use a decent Solar Charge Controller and you’ll have no issues. It can tell when your batteries are fully charged vs. not and manage everything automatically. But again, you’ll want to verify if your rig is 12V or 24V first.

  8. PEEWEE HENSON Reply

    RICH, THAT’S ABOUT THE BEST SCHOOLING ON BATTERIES I’VE FOUND. WHEW, SIMPLE IS ALWAYS GOOD. HERE’S MY DILEMMA; I’M RUINED 2 SETS OF BATTERIES AND NO ONE AT ANY RV SHOP I VISITED WAS HELPFUL. I’M BUYING A PAIR OF 6 VOLT TROJANS AND A NEW 4 PHASE CONVERTER/CHARGER. I ATTEMPT TO PLUG INTO SHORE POWER WHEN I CAN TO SAVE BATTERY LIFE. BUT IF I DISCONNECT THE BATTERY WHILE CONNECTED TO SHORE POWER NOTHING WORKS. IS THIS A UNIQUE PROBLEM OR IS THIS HOW ITS SUPPOSED TO BE OR MY ORIGINAL CONVERTER/CHARGER IS JUNK? THANKS FORM THE HELP PEEWEE HENSON RENO, NV

    • Rich Reply

      Hi Peewee – I’m guessing that either your original converter/charger is bad – or it’s wired incorrectly. In our case while plugged into shore power the power goes to the converter/charger first – which supplies 45amps worth of 12volt power to the RV. If there are no batteries present, we still have 12-volt power from the converter. If batteries are present, the converter/charger also chargers the batteries in 4 stages. It might also be a bad fuse – some converter/chargers have fuses mounted right on them and sometimes they’re mounted on the main fuse board.

      Either way, you’ll be much better off with a new 4-stage converter/charger. Good luck!

    • Rich Reply

      Hi Jason – RV generators use the chassis battery – the RV starter battery – to start. Not the house batteries (the Trojans).

  9. larry clifton Reply

    hey i need help i dont have a lot of money on budget just purchased a used 21ft rv i want to go to 2 12v batteries instead of one i was looking at decabe battiers says 1000 amps can you recomend a decent inverted to replace my stock one and if this battery isnt what i need could you recomend one

    • Rich Reply

      Hi Larry – if you’re on a budget why go to 2 batteries? I only recommend using batteries from Trojan, Crown, or Lifeline. I use 2x Trojan T105s and have had excellent results from them. I can boondock a weekend (2-3 days) between charges easily – although I don’t watch much TV. I don’t recommend other batteries simply because I don’t have experience with them.

      As far as a decent inverter – I haven’t used many, but I’ve heard reasonably good things about Go Power! Inverters. Pure Sine Wave inverters are quieter and more efficient. Ideally you’ll use an inverter just big enough to handle what you need – if you’re only use 100 watts a 2000 watt inverter is overkill. Also, a larger inverter will waste more power due to parasitic loss. So figure out your max usage – and I’d probably go with either this 150 Watt Pure Sine Wave unit. There’s a link on the same page to the 300 watt unit – or bigger if you need it.

  10. John Thien Reply

    How important is Cold Cranking Amps in choosing battery? I have a 5th wheel with no generator, so don’t need to “start” anything. I currently use a 24DC with 92 AH @ 1A and Marine Crank Amps of 690.

    • Rich Reply

      Hi John – Cold Cranking Amps aren’t important for Deep Cycles at all – which is why they’re not recommended for Starter Batteries. CCA is largely a measure of how quickly the battery can produce power. It’s also a quick discharge that relies on the vehicle alternator to replenish quickly. You want house batteries that discharge relatively slowly as they store power better for longer = deep cycle batteries.

      The 92AH @ 1A sounds like a WalMart battery. I’ve only ever seen WalMart use the @1A measure. Everyone else uses @20A. That battery should be fine if you stay plugged in, but if you go off grid I wouldn’t expect it to last long (hours). Good luck!

  11. In your Series/Parallel diagram, the wording is not correct under the Parrallel photo. Should be “in parrallel” not “in series”.
    Otherwise, a great article on batteries!
    Happy travels ….

    • Rich Reply

      Ah – in the small text. Good catch, I’ll fix it. Thanks!

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