Dear Dave,
Readers appreciate very much your RV tech wisdom. Could you provide an article on the various battery types available for RVs, those useful for solar power when off-grid and what all the acronyms mean? Thanks. —Colin, 2020 Jayco 26.7
Dear Colin,
Thank you for your kind words. This is a very popular subject, as most traditional RVers have had issues with the standard house batteries for years. Typical lead acid batteries last about 2-3 years, if that, and should last 5-7.
Types of batteries
FLA
For years, Flooded Lead Acid (FLA) batteries have been the mainstay for house batteries as they are deep cycle, which means they can be drawn down and recharged hundreds of times. They have lead plates inside that are covered by an acid solution and store electricity.
The two main types of FLA batteries that are used are 12-volt deep cycle and 6-volt deep cycle. The 6-volt batteries require two batteries connected in series, which is positive to negative, that gives you a 12-volt “bank.” Smaller RVs can use just one 12-volt battery to power the DC components such as lights, roof vents, water pump, and other items, while you will need two 6-volt batteries to do the same. Connecting the 6-volt batteries in series does not double the amp hours, just the voltage.
The main advantage of the 6-volt batteries is with more plates comes more longevity which means more cycles and longer lasting… IF you maintain them properly, which we will cover in a bit. The main disadvantage is needing two batteries, so more room, weight, and expense. And if you want to add more amp hours, you will need two more batteries.
The main advantage of a 12-volt battery is you only need one, meaning less space and money. Plus, you only need one to double the amp hours. The main disadvantage is less cycles with less plates.
Disadvantages of FLA batteries
FLA batteries can be used for boondocking or dry camping and solar. However, they can only be drained to 50% of the available amp hours so they need to be recharged more often. They come in a variety of sizes or amp hour ratings such as Group 24, 27, 31, and others, which is approximately 115 amp hours up to 180 amp hours. But again, they can only be drawn down 50%.
Another disadvantage of FLA batteries is sulfation. When the power is drawn from the battery, sulfur coats the plates and requires a multi-stage charger to break up the sulfation during the initial bulk charging stage, which many converter/chargers do not have. As the sulfur gets thicker, the battery’s ability to store power is diminished. So without a proper charger, the batteries only last a fraction of the time they should. And they need to be checked for fluid levels more often as the charging boils the acid and it gases out the vents. Understanding the limitations and proper maintenance/charging can provide the cheapest solution for 12-volt DC power.
AGM
Absorbed Glass Mat (AGM) is another version of a 12-volt or 6-volt battery that has plates and acid. However, it is completely sealed and has fiberglass mats that separate the positive and negative plates and absorbs the acid. They are less prone to sulfation and have less gassing, so there is less acid loss. They typically last longer due to less sulfation, but are more expensive and do not provide any more amp-hour capacity than similar rated FLA types. But they are a better option for boondocking due to less sulfation and longevity.
LiFePO4
LiFeP04 stands for Lithium (Li) Iron (Fe) and Phosphate (PO4), i.e., Lithium Iron Phosphate batteries. They are often mistakenly called Lithium Ion batteries. Lithium Iron Phosphate batteries will last 4x longer. Lithium batteries are one of the hottest products in the RV market, but also very expensive. However, if you plan to boondock and do it for a long period of time, they will typically pay for themselves over the 10-year warranty period and provide superior 12-volt power as they can be drained to almost 100%.
The advantage is no sulfation, no gassing, limited maintenance, more than 3,000 cycles and a 10-year warranty, as well as more available 12-volt power. The disadvantage is the price and the specific need for continuous 14.6-volt charging, which a typical converter will not provide. Also, it can’t be charged below freezing temperatures, and cannot be charged with a multi-stage charger. You cannot just swap out a set of FLA batteries with LiFePO4 without researching the type of converter, solar panel charge controller, and a superior Lithium Battery with a Battery Management System (BMS).
There is a lot of junk out in the market designed for stationary systems such as residential solar, so it is important to look for a quality Lithium battery manufacturer such as Expion 360, Go Power, and Battleborn, just to name a few. Check out the cells, mechanical connections, and BMS in the article posted here.
You might also enjoy this from Dave
What RV batteries do you recommend for both chassis and house?
Dear Dave,
What RV batteries do you recommend for the chassis and house? My rig has sat in dry storage for two years and after a jump it doesn’t seem to be recharging. Do “any” Group 24 batteries work for the chassis and “any” Group 31 work for the house? There are two of each. —Kevin, 1999 Fleetwood Discovery
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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…And one other category, VRFLA — Valve-Regulated Flooded Lead-Acid. These are batteries that appeared in the mid 60s or so, and have that “Green Eye” indicator on them. They are not designed to have water added.
Our Roadtrek SS Agile uses four of these (6V @ 190AH), also referred to as “Golf Cart” batteries, in a series-parallel arrangement to get 12V. I feel these are the best — no temperature limited charging, no fancy charging apparatus required, essentially no maintenance required.
Needs differ of course, but for me, AGM offers the best bang for the buck for either starting and deep cycle applications. For deep cycle, I can still use the OEM converter for charging, and the batteries work/recharge in sub-freezing temps. Even here in south Texas we see winter freezes (as shown in recent news). But most of all, my batteries are not easy to access to perform routine maintenance like adding water. For both starting and deep cycle types, I have batteries that sit untended, other than a batteryminder, for months at a time. (a car in storage up north for the winter and a travel trailer in storage down south for the summer).
I jumped into the Lithium battery swap before realizing the problems with cold weather charging (or lack thereof). I hadn’t planned to camp in freezing temps but got thrust into it with some unexpected freezes in places that ordinarily DO NOT freeze. Silly me. I talked to tech reps at Expion who advised that it would be a good idea to disconnect my batteries and the charging during freezing temps. Even though they have a BMS built in to prevent charging below freezing, it’s not a good idea to have a charger pounding at the batteries when the BMS is preventing charging. Also, it’s not advised to store the batteries fully charged. It’s better to draw them down to about 70% and let them sit.
l drew them down, shut off the solar panels – and disconnected the batteries so I could run the onboard converter when plugged into shore power and not have it trying to charge the batteries. I finally installed knife switches on my batteries, making them easier to disconnect. Who knew?
I believe some Battleborn batteries have a built-in heater to allow cold weather charging, sorry.
You are right, james. I watched a video on Battleborn’s site showing how you hook that option up. Expion offers warming ‘kits’ that you can put their batteries into that do the same thing. Problem for me is, when they installed my batteries with the myriad wires, and strapped the batteries to the floor, it is almost impossible for my aging body to crawl into that space and disconnect all this stuff to wrap the batteries. I’ll pay someone to do it. Better yet, I’ll try NOT to get stuck in freezing temps. Ha.