Short answer: for most touring setups, lithium (LiFePO4) is the better battery. You can use more of what it holds, it weighs a fraction as much, and it lasts many more cycles. AGM still has a place where the battery has to charge in freezing weather, in a small light-use setup, and on price.
Here's where that answer comes from.
How much of the battery can you actually use?
This is the big one, because the number on the case isn't what you get.
AGM. Victron's advice for all lead-acid is not to take it below half, and to get it back to full regularly, about every 30 days. So a 100 Ah AGM gives you about 50 Ah if you want it to last.
Lithium. Victron rate their Lithium Battery Smart at 2500 cycles when you take 80% out each time, so 80% is a fair working figure. And unlike lead-acid, it doesn't need a full charge. Victron say service life "even slightly improves" with partial charging.
There's a quieter catch with AGM too: the harder you pull, the less you get. Victron's table shows an AGM drained over one hour gives only 65% of its rated capacity. Run a kettle or a coffee machine through an inverter and an AGM gives you less than the case says.
What about "100% usable"?
Exotronic advertise their Alpha batteries as 0-100% usable. Their own manual recommends keeping them between 10% and 90% to extend service life. So you can use it all, but if you want it to last, plan on about 80%.
How long does each one last?
Cycle life is how many times you can drain and recharge a battery before it's worn out. The makers rate it at different depths, so here they are side by side:
| Battery (maker's figures) | Deep use | Middle | Light use |
|---|---|---|---|
| Victron 12 V Deep Cycle AGM | 400 cycles at 80% | 600 at 50% | 1500 at 30% |
| Victron 12 V Deep Cycle GEL | 500 cycles at 80% | 750 at 50% | 1800 at 30% |
| Victron Lithium Battery Smart | 2500 cycles at 80% | 3000 at 70% | 5000 at 50% |
| Exotronic Alpha 100Ah Slimline and 180Ah IP67 | over 3000 full (100%) cycles at 25°C, to 80% capacity within 5 years |
Victron count their lithium cycles until the battery is down to 80% of its original capacity. Either way, the deeper you go each time, the fewer cycles you get.
Lead-acid also hates sitting partly flat. If it's rarely fully charged or left discharged, it fails early from sulfation. On a trip with a few cloudy days, that's hard to avoid.
What about weight?
This is where lithium pulls right away. From the makers' datasheets:
- Victron 12 V Deep Cycle AGM: 90 Ah is 27 kg, 110 Ah is 32 kg, 220 Ah is 65 kg.
- Victron Lithium Battery Smart: 100 Ah is 14 kg, 200 Ah is 20 kg.
- Exotronic Alpha: 100Ah Slimline is 11.7 kg, 180Ah IP67 is 17.5 kg.
Victron claim their lithium saves up to 70% in weight, and the same in space.
An illustration, using Victron's figures
Say you're choosing between Victron's 220 Ah AGM and their 200 Ah Lithium Battery Smart:
- AGM: 220 Ah x 50% = 110 Ah usable, at 65 kg. About 0.59 kg per usable Ah. At 50% discharge it's rated for 600 cycles: 600 x 110 = about 66,000 Ah over its life.
- Lithium: 200 Ah x 80% = 160 Ah usable, at 20 kg. About 0.13 kg per usable Ah. At 80% discharge it's rated for 2500 cycles: 2500 x 160 = about 400,000 Ah over its life.
That's our arithmetic, not a rating, and real life (heat, charging, how often you actually cycle it) will move both numbers. But the gap is big enough that the direction is clear. On a 4WD that's already near its payload, 45 kg is a lot of water, food or recovery gear.
Can you charge lithium in the cold?
Not below about 5°C, and this is the one area where AGM is genuinely easier.
Victron's Lithium Battery Smart charges only between +5°C and +50°C, and discharges from -20°C to +50°C. Their manual is blunt about it: "A lithium battery cell will sustain permanent damage when charged at temperatures below 5°C."
Exotronic list the Alpha 100Ah Slimline and 180Ah IP67 as charging between 5°C and 45°C, and discharging from -20°C to 55°C. Their pages don't say whether the BMS blocks charging below 5°C on its own, so if you camp where it freezes overnight, check with Exotronic before you rely on it.
Lithium also gives less in the cold: Victron's 100 Ah is rated at 80 Ah at 0°C and 50 Ah at -20°C.
AGM isn't trouble-free in the cold either. Victron give no charging cut-off, but want the charge voltage temperature-compensated if the battery sits below 10°C or above 30°C for long periods, and its capacity drops sharply when it's cold.
And in the heat?
Heat matters too, and plenty of Australian touring happens in it. Victron say high temperature is very bad for AGM service life: their design float life is 7 to 10 years at 20°C, 4 years at 30°C and 2 years at 40°C. A battery in a canopy or a van in the northern summer spends plenty of time at the hot end of that. Victron's lithium limit for charging and discharging is +50°C; Exotronic give 45°C for charging and 55°C for discharging.
What if the rig sits in the shed between trips?
- AGM: Victron give a self-discharge under 2% a month at 20°C, doubling for every 10°C warmer. It also wants a full charge regularly to avoid sulfation.
- Lithium: Victron's Lithium Battery Smart documents don't give a self-discharge figure, but their Lithium NG documents do, and they disagree with each other. The NG datasheet's front page says a maximum of 2% a month; its own spec table says up to 3% a month at 25°C, and the NG manual says a maximum of 3% a month. Either way it's low.
- Exotronic Alpha: charge it once every 3 months in storage. Ideal storage is 25°C at 40% charge (about 13 V).
One warning worth taping inside the battery box. After the BMS cuts out on low voltage, Exotronic say "the battery must be charged within 72 hours after a low voltage trip", or it may not recover. A small standing load that flattens the battery while the van's parked can do exactly that, so an isolator or a trickle of solar is worth having.
What does the BMS limit?
A lithium battery's built-in battery management system (BMS) sets how hard you can push it, so check it against your biggest load before you buy. Exotronic's figures:
| Alpha 100Ah Slimline | Alpha 180Ah IP67 | |
|---|---|---|
| Continuous discharge (30 min) | 100 A | 200 A |
| Largest inverter | 1000 W | 2000 W |
| Charge current, nominal / maximum | 30 A / 50 A | 50 A / 85 A |
If you want a 2000 W inverter, the Slimline isn't the battery for it on its own. (Watts vs VA is in our inverter guide.) The 180Ah isn't meant for under the bonnet or as a cranking battery.
On fusing, Exotronic say to fuse the battery's output positive with a fuse no bigger than 2C, which on a 100 Ah battery means no bigger than 200 A, and that it's to be installed by a competent person. Never bypass a BMS or fuse to get more out of a battery. Our fusing guide covers where the fuses go.
So when does AGM still make sense?
- You need to charge below 5°C and don't want to manage a lithium battery's cold limits.
- A small, light-use setup that rarely goes below half and gets charged to full often (a powered site, or a charger at home), where the weight doesn't matter much.
- Price. Compare, say, the Victron 110Ah AGM at $569.95 with the Exotronic Alpha 100Ah Slimline at $694.95 or the Victron 100Ah Smart LiFePO4 at $1,009.95, and weigh it against the usable capacity and cycle life above.
For anything that lives on the road, our pick is lithium, and it's what we run in our own van. Work out how much you need first with our sizing guide, and if you're charging lithium from a modern vehicle, read smart alternators and DC-DC chargers before you wire it up. Both types are in our batteries range.