AGM vs lithium
Lithium gives you more usable power, and AGM costs less upfront.
Lithium lets you use about 85% of its rated capacity, and it weighs less for the same Ah.
AGM costs less to buy, but only about 45% of its rated capacity is usable.
Updated . 9 min read • Technical Guide
Lithium lets you use most of its rated capacity and weighs less. AGM costs less upfront, but only about 45% of its capacity is usable.
Compare them on usable capacity, which is how much of the label figure you can actually draw.
- Usable capacity, AGM - about 45% of rated (long-life rule of thumb; check your battery's own datasheet)
- Usable capacity, lithium - about 85% of rated (typical manufacturer guidance)
Compare batteries on usable capacity
Two batteries can carry the same Ah rating on the label and still give you very different amounts of energy you can actually use. The difference is how deeply you can drain each chemistry before it counts as flat.
As a long-life rule of thumb, AGM and flooded lead-acid batteries are best used to about 45% of their rated capacity, with the usual charging and conversion losses on top. Lithium is built to be discharged much further, so a typical planning figure is about 85% of rated capacity. That gap is the single biggest reason a lithium upgrade can feel like a much bigger battery even at the same Ah number.
Compare in watt-hours
Multiply the rated Ah by the bank's voltage (12, 24 or 48) to get watt-hours, then apply the usable fraction above. A 200Ah AGM bank is about 2,400Wh rated but roughly 1,080Wh usable. A 200Ah lithium bank is the same 2,400Wh rated but roughly 2,040Wh usable, which is why the same number on the box does not mean the same battery.
AGM, in plain terms
AGM (absorbent glass mat) is a sealed lead-acid battery, the same family that has powered caravans for decades. It needs no special charger, tolerates a wide range of temperatures reasonably well, and is generally the cheaper option to buy upfront.
The tradeoffs are weight and usable capacity. AGM is heavier than lithium for the same rated Ah, and repeatedly discharging it much past about 45% of its rated capacity shortens its working life, so the practical capacity is smaller than the label suggests.
Lithium, in plain terms
The lithium in caravan batteries is usually LiFePO4 (lithium iron phosphate). Caravans use it because it is stable and lasts many charge cycles. Lighter lithium types exist. It is lighter than AGM for the same rated Ah, can be discharged much further without shortening its life, and is generally rated for a far higher number of charge cycles.
The tradeoffs are cost and compatibility. Lithium costs more upfront than AGM at the same Ah rating. It generally needs a charging system, a solar controller and a battery management system that suit it. That is why swapping one into an older van is a job for a qualified auto electrician.
What one looks like as a fitted battery
The B1232 from BLUETTI is a 12.8V 314Ah LiFePO4 battery. It holds about 4,019Wh on the label and adds 29.3kg to your payload. Multiply the volts by the amp-hours of any battery you are shown, and you can compare it with your own van in watt-hours.
BLUETTI is a partner we earn a commission from if you buy through the link below. We earn nothing from the comparison above, which is why the chemistry sections name no brand at all.
Where the battery choice meets your payload
A bigger, heavier battery bank is still weight the van has to carry, on top of water, gas and everything else in your allowance. Whichever chemistry you choose, the battery's weight comes out of the same payload figure.
Caravan weights explained walks through ATM, Tare and payload with real numbers, and off-grid caravan capability covers how water, power and payload trade off against each other on a real trip.
Battery type questions, answered
What battery is best for a caravan?
Lithium for full-time or heavy off-grid use. AGM for a few weekends a year. You can use about 85% of a lithium battery's rated capacity, and it weighs less for the same usable capacity. AGM costs less to buy, and about 45% of its capacity is usable. Compare any two batteries on usable watt-hours.
How long does a caravan battery last?
On one charge, a battery lasts its usable watt-hours divided by what you use in a day. A 100Ah battery on a 12V system holds about 1,200Wh on the label. That is about 1,020Wh usable as lithium and about 540Wh as AGM. At a made-up daily use of 500Wh, that is about 2 days for lithium and 1.1 days for AGM with no charging. Over its working life, a lithium battery is generally rated for many more charge cycles than AGM. How long any one battery lasts depends on how it is used, charged and looked after.
Is lithium always better than AGM for a caravan?
No. Each one suits a different kind of trip. Lithium gives more usable capacity for its weight and handles a deeper, more frequent cycle of charging and discharging, which suits full-time or heavy off-grid use. AGM costs less to buy and is a known, simple technology, which suits a van used a handful of weekends a year where the extra usable capacity is not worth as much.
Why does usable capacity matter more than the rated Ah figure?
Because the rated figure and the amount you can actually draw down without shortening the battery's life are two different numbers. A lithium battery is built to be discharged much further than an AGM battery before it is considered flat in practical terms, so two batteries with the same Ah rating can deliver very different amounts of usable energy. Compare batteries on usable watt-hours.
Can I replace an AGM battery with lithium in the same caravan?
Often, but not automatically. Lithium generally needs a compatible charging profile from the solar controller, the vehicle charger and any mains charger, and a battery management system suited to the chemistry. Get this checked by a qualified auto electrician before swapping chemistries rather than assuming the existing wiring and chargers are already set up for it.
Do lithium batteries really last longer than AGM?
Lithium batteries are generally rated for many more charge and discharge cycles before their capacity drops to a stated share of new. That is the main reason they cost more upfront and less over a long ownership. How long any individual battery actually lasts still depends on how it is used, charged and looked after, so treat a cycle rating as a guide only.
How much does battery chemistry affect a caravan's weight?
A lot, for the same usable capacity. Lithium cells store more energy per kilogram than AGM, so a lithium battery delivering the same usable watt-hours as an AGM bank typically weighs a good deal less. That weight difference comes straight off, or back onto, your payload allowance, which matters more the more battery capacity you are carrying.
Take the battery choice out to a real trip
See how the battery figure fits alongside water and payload for genuine off-grid capability.