- A word on Lithium (LiFePO4) Batteries
- RV Battery Converter Charger – The cause of most RV Battery problems
- The Solution: The Smart (4-Stage) Battery Charger / Converter
- Battery Amp Hours Explained
- The Common Types of RV Batteries
- Our RV House Battery Setup
- How Lead Acid Batteries Work
- How to Damage or Ruin RV Batteries
- How to Maintain Lead Acid Batteries
Recreational Vehicles – RVs – are designed to work with or without hookups (power, water, and sewer). This is possible in large part due to RV ‘house’ batteries that power interior lights, water pump, vent fans, and the power inverter (if you have one) – which allows you to plug in and use 120-volt electronics.
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 in their first year of 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.
I’ll just cover the basics, which is still quite a lot of information, and hopefully this article will help you find the right battery setup for your RV. Bear with me, as I’ll get fairly technical in a few areas, but it’s worth knowing about batteries when it comes to RVing!
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 →
A word about 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.
RV Battery Single Stage Converter Charger – The cause of short House Battery life and other problems.
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 the 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 everything 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.
The problem is that many factory-installed converters charge and maintain batteries at a consistent voltage – usually 13.6V to 13.8V – which 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 3 or 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.
Converters & Generators
Single-stage converters also make charging RV house batteries with your generator expensive and mostly pointless. Charging the batteries from 50% discharge at 13.7 Volts takes forever without the higher voltage bulk and absorption stages that a smart converter provides.
If you plan to boondock and charge your batteries by generator, upgrading to a smart converter charger is a must.
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. The charger literally boils off some of the water in the batteries, which speeds up the sulfation process and the batteries require more frequent maintenance – or 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.
Finally, keeping the batteries at a 13.2V float charge keeps them cooler and they require less maintenance (water) as a result. This also prevents excessive sulfation, which is the death of any lead acid battery.
The Solution: The Smart (4-Stage) Battery Charger / Converter
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 reality is, this problem is almost 100% due to the low-quality battery charger/converters that are installed in most RVs.
With a proper 4-stage smart converter/battery charger, batteries like our Trojan T105s and Lifelines can last 7 – 10 years – or even longer depending on use, care, and number of cycles.
That’s a potential savings of hundreds of dollars every year or two, plus your batteries will actually work for a change! 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 all night (since the water pump runs on batteries).
This situation is standard for us now that I installed our Iota Smart 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 converter first, and then replace the batteries if they aren’t holding a charge from your new smart converter/charger.
Battery Amp Hours explained
Before I get into battery types, I think it’s helpful to cover battery amp hours. Amp Hours are the best and most common way to measure battery storage capacity, so think of Amp Hours (AH) like your battery gas tank.
Simply put, 1 amp hour (1AH) is the amount of power it takes to power a 1 amp draw for 1 hour. An LED light typically pulls .5 AH, so 6 lights = 3 AH. If you have 100AH of available charge, you could run those 6 lights for just over 33 hours. 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 used because batteries supply more total Amp Hours when 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
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
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
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.
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.
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
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’re 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 batteries 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 them and keeping the terminals clean.
For flooded lead-acid batteries -including golf cart batteries – regular charging and occasional watering are necessary.
Very 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.
To ensure that you get the water into the battery, it’s helpful to use a battery filler. It looks like a big turkey baster. I’ll make a video about this soon – although it’s pretty easy. 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 cells should typically be filled up to 1/8-inch below the lip. There’s no need to measure, just fill it until it’s just below the lip, as an 1/8 inch is very small. Then close that cell and move on to the next one.
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!