LiFePO4 vs AGM batteries for an RV

Most RV and van battery decisions come down to two chemistries: LiFePO4 (lithium iron phosphate) and AGM (sealed lead-acid). The biggest practical difference is not the label on the case. It is how much of the rated capacity you can actually use, and that changes how many amp-hours you need to buy.

RVWatt sizes a battery bank as daily watt-hours × days without charging ÷ usable depth of discharge. The calculator uses 80% usable for LiFePO4 and 50% for AGM, the same planning figures most battery makers and sizing guides use. It also counts charging losses: about 5% for LiFePO4 and 15% for AGM.

Usable capacity is the big difference

A 12 V 100 Ah battery stores about 1,200 Wh on paper. At 80% usable, a LiFePO4 battery gives you about 960 Wh. At 50% usable, an AGM battery gives you about 600 Wh. You can pull an AGM deeper than half, but regularly doing so shortens its life, which is why the calculator plans around 50%.

So for the same day of use, an AGM bank has to be about 1.6 times the rated amp-hours of a LiFePO4 bank (0.8 ÷ 0.5). Here is what that looks like with the calculator’s presets, two days of reserve at 12 V:

Rig, place and season	Daily use	LiFePO4 bank	AGM bank	Solar needed, LiFePO4	Solar needed, AGM
Weekender van, Denver, May–October	830 Wh	173 Ah (2,075 Wh)	277 Ah (3,320 Wh)	276 W	308 W
Full-time van, Hailey, ID, July only	2,103 Wh	438 Ah (5,258 Wh)	701 Ah (8,413 Wh)	361 W	404 W
Class C motorhome, Denver, April–October	2,542 Wh	530 Ah (6,356 Wh)	847 Ah (10,170 Wh)	844 W	943 W

The bank sizes are rated capacity, the number printed on the battery. In practice you round up to whole batteries: the weekender’s 173 Ah is usually a 200 Ah lithium bank, while the AGM version needs about three 100 Ah batteries.

Weekender van with LiFePO4 Same van with AGM

Charging losses mean a little more solar for AGM

With the default losses and an MPPT controller, about 75.7% of a panel’s rated watts × peak sun hours ends up stored in a LiFePO4 bank. With AGM that drops to about 67.7%, because more energy is lost as heat while charging. That is why the AGM column above needs roughly 12% more solar for the same day.

There is a second, practical issue the averages do not show. Lead-acid batteries need a long, slow absorption stage to get truly full, and they age faster when they sit partly charged day after day. On a cloudy stretch, a modest solar array often cannot finish that last part of the charge. LiFePO4 does not mind sitting at partial charge, and it accepts charge quickly until it is nearly full.

Big loads: inverters, microwaves and coffee makers

High-current loads expose another difference. The calculator warns when, at full inverter output, the bank would be asked for more current than is comfortable: about 1C for LiFePO4 (100 A from a 100 Ah battery, subject to its BMS rating) and about 0.2C for AGM (20 A per 100 Ah).

The Class C example shows it. Its 2,500 W inverter can pull about 265 A from a 12 V bank at full output. The 530 Ah lithium bank handles that. The 847 Ah AGM bank is only comfortable to about 170 A, so the calculator flags it, even though the AGM bank is much larger in amp-hours. AGM batteries also deliver less than their rated amp-hours at high discharge rates (the Peukert effect). The calculator does not model that, which is one more reason to keep AGM at 50% usable and treat the result as a minimum.

If you plan to run a microwave, an induction cooktop or an electric kettle off the batteries, see what size inverter for an RV for how the inverter and its cable are sized.

Weight and space

Weight is where many RVers notice the change first. Manufacturer spec sheets for 12 V 100 Ah batteries commonly list roughly 60–70 lb for AGM and roughly 20–30 lb for LiFePO4. Combine that with the usable-capacity gap and an AGM bank can weigh several times as much as a lithium bank that delivers the same usable energy. Check the spec sheet for the batteries you are actually considering, and check your rig’s cargo capacity and battery-compartment limits.

Cold weather

Most LiFePO4 batteries must not be charged below 0 °C (32 °F). Charging them while frozen can permanently damage the cells. Many have a BMS that blocks cold charging, and some have built-in heaters. RVWatt warns you when NASA’s record low temperatures at your location dropped below freezing in a month you travel. For example, Denver has recorded lows below freezing in May, September and October over 2001–2025. Those are the coldest readings in each month, not a typical night, but one cold night is enough to matter.

AGM batteries can generally accept a charge below freezing at a reduced rate, ideally with a temperature-compensated charger. Both chemistries deliver less capacity when cold, and the calculator does not model that loss. If you camp in real winter conditions, choose a self-heating lithium battery or keep the bank inside the heated living space, and leave extra margin.

Cost over the life of the battery

LiFePO4 costs more up front per rated amp-hour. It is usually rated for many more charge cycles at a deeper depth of discharge than AGM. The fair comparison is cost per usable kilowatt-hour over the battery’s expected cycle life, using the depth of discharge and cycle rating from each battery’s own datasheet, not marketing copy. For a rig that is used a few weekends a year and plugged into shore power the rest of the time, AGM can still be the cheaper choice. For full-time or frequent boondocking, lithium usually comes out ahead.

Switching from AGM to lithium

Changing chemistry is not just a battery swap. Check that each charging source has a LiFePO4 setting or profile: the RV’s converter/charger, the solar charge controller and any DC-DC charger. An alternator charging a large lithium bank directly can be overloaded, which is why a DC-DC charger is the usual choice. Do not mix chemistries, or old and new batteries, in one bank.

Lithium banks can deliver very high short-circuit current. Put a fuse rated for that current (often a Class T for lithium) on the positive cable as close to the battery as practical, use cable sized for the fuse, and follow the battery maker’s instructions on BMS limits and paralleling. If you are not confident, have a qualified RV or marine electrician do the work.

When AGM still makes sense

AGM is a reasonable pick when you mostly camp with shore power or a generator, use the rig only occasionally, need to charge below freezing without a heated space, or have a tight budget and a light daily load. Everyone else, especially anyone who boondocks for days at a time, will usually be happier with LiFePO4. Either way, start from your real daily watt-hours: the appliance wattage chart and the fridge guide are good places to begin, and the camper van guide shows full worked examples.

Size your own battery bank in the calculator

Frequently asked questions

Is a 100 Ah lithium battery the same as a 200 Ah AGM?

Close, in usable energy. RVWatt plans on 80% usable for LiFePO4 and 50% for AGM. A 12 V 100 Ah LiFePO4 battery gives about 960 Wh, and a 200 Ah AGM bank gives about 1,200 Wh at 50%, so 100 Ah of lithium sits between 150 Ah and 200 Ah of AGM. The AGM bank will be much heavier, needs a little more solar because of charging losses, and handles high inverter current less comfortably.

How much more battery do I need with AGM?

About 1.6 times the rated amp-hours, because 0.8 ÷ 0.5 = 1.6. The weekender van preset in Denver from May to October needs 173 Ah of LiFePO4 or 277 Ah of AGM for two days at 12 V. It also needs a little more solar with AGM, 308 W instead of 276 W, because lead-acid loses more energy while charging.

Can I charge a LiFePO4 battery below freezing?

Usually not. Most LiFePO4 batteries must not be charged below 0 °C (32 °F). Use a battery with a built-in heater or low-temperature charge protection, or keep the bank inside the heated living space. AGM can generally take a reduced charge in the cold. Both chemistries give less capacity when cold.

Do I need new chargers if I switch to lithium?

Often yes, or at least new settings. Check that the converter/charger, solar charge controller and any DC-DC charger have a LiFePO4 profile, and protect the alternator with a DC-DC charger instead of wiring a large lithium bank straight to it. Fuse the battery for its short-circuit current, often with a Class T fuse.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.