Battery Basics
Lithium vs AGM Batteries for Your RV
Both will keep your lights on. Only one of them changes what you can run off-grid. Here is the difference in plain terms, and how to tell which one you need.
The short answer
If you camp with hookups most of the time, AGM batteries are a sensible, lower cost choice. If you want to spend real time off-grid, run heavy appliances on battery power, or stop relying on a generator, lithium is the one that gets you there.
The reason comes down to one idea: the amp hours printed on the label are not the amp hours you get to use. It is also a common reason RV batteries die overnight.
Lithium vs AGM, side by side
| What matters | AGM | Lithium |
|---|---|---|
| Usable capacity | About half of the rated amp hours if you want the bank to last | Most of the rated amp hours, day after day |
| Weight | Heavy. A large bank can add hundreds of pounds | Roughly half the weight or less for the same rated capacity |
| Charging | Slows down sharply as it fills, so the last stretch takes hours | Accepts charge quickly almost all the way to full |
| Voltage under load | Sags as the bank drains and when a big load starts | Stays steady through most of the discharge |
| Lifespan | Typically hundreds of cycles, fewer if drained deeply | Typically thousands of cycles |
| Upfront cost | Lower | Higher |
| Cold weather | Loses capacity in the cold but can still be charged | Should not be charged below freezing without protection or heating |
These are typical traits of each battery type. Exact figures vary by manufacturer and model. The lithium batteries used in RVs are lithium iron phosphate, often written LiFePO4.
Usable capacity is the number that matters
An AGM battery is a sealed lead acid battery. Drain it much past halfway on a regular basis and it wears out early. So a 400 amp hour AGM bank realistically gives you about 200 amp hours before you should stop and recharge.
A lithium bank with the same 400 amp hour rating lets you use most of it without that penalty. Same label, close to twice the energy you can actually spend. That is the whole comparison in one sentence, and everything else follows from it.
What it means once you are parked
Steady voltage is the part people feel first. As an AGM bank drains, its voltage drops, and a big load pulls it down further. Inverters shut off, microwaves run weak, and things that worked at sunset stop working at midnight. Lithium holds its voltage through most of the discharge, so appliances behave the same late at night as they did in the afternoon.
Charging is the second. An AGM bank takes charge quickly at first and then slows to a trickle for the last stretch, which is why a few hours of sun or generator time often leaves it short of full. Lithium takes charge quickly nearly the whole way, so a good solar day actually refills what you used the night before.
Weight is the third. Building a large AGM bank can add hundreds of pounds to a coach. The same usable energy in lithium weighs a fraction of that and takes up less space in the compartment.
When AGM is the right call
AGM is not obsolete. It makes sense when you are plugged in most nights, when your battery loads are light, and when you only need to cover short stops and travel days. It costs less up front, it works with the charging equipment most coaches already have, and it can be charged in freezing weather.
If that describes how you camp, spending more on lithium buys you capacity you may never use.
When lithium is worth it
Lithium earns its cost when you camp without hookups for days at a time, when you want to run a residential refrigerator, a microwave, or an air conditioner on battery power, or when you are tired of running a generator to get through the night. It also lasts through far more charge cycles, so the higher price is spread over many more years of use.
Running air conditioning on batteries takes more than the batteries, though. It needs an inverter sized for the startup surge and enough solar to refill the bank. We cover that on the page about running your RV AC without a generator.
Switching from AGM to lithium
Lithium is not a drop-in replacement. It charges at different voltages, so the converter, the solar charge controller, and the engine charging circuit all have to be set up for it. It can also deliver and accept much higher current than the old bank, which means cabling and fusing need to be checked. And because lithium should not be charged below freezing, where the bank sits and how it is protected matters.
That work is what our RV lithium battery installation covers. If you are not sure how much battery you need, the solar calculator gives you a starting point based on what you want to run.
Can I just swap my AGM batteries for lithium?
Not as a straight swap. Lithium charges at different voltages than AGM, so the converter, the solar charge controller, and engine charging all need to be checked and set up to match. Cabling and fusing may need to change too.
Can I mix AGM and lithium in the same bank?
No. The two chemistries charge and discharge differently, and wiring them together shortens the life of both. Pick one for the house bank.
Is AGM ever the better choice?
Yes. If you are plugged in at a campground most nights and only need batteries for lights, the water pump, and short stops, an AGM bank does that job for less money.
Will lithium run my air conditioner?
A lithium bank is what makes it realistic, but the batteries are only one part. The inverter and the solar that refills the bank have to be sized for it as well.
Not sure which one you need?
Tell us about your coach and how you camp. A technician will follow up with an honest answer, including when your current batteries are fine.