Your battery bank is the heart of a van power system. Here is how lithium iron phosphate and AGM lead-acid really compare.
LiFePO4 (lithium iron phosphate) is the modern standard for van builds. AGM (absorbent glass mat) is the older lead-acid technology that is cheap but limited. For most people building a new van, the choice is now clear.
| Factor | LiFePO4 (lithium) | AGM (lead-acid) |
|---|---|---|
| Usable capacity | 80 to 100% of rated | About 50% (don't deep-discharge) |
| Cycle life | 2,000 to 5,000+ cycles | 300 to 700 cycles |
| Weight for same power | Much lighter | Heavy |
| Cost upfront | Higher | Lower |
| Best for | Full-time, daily use | Budget weekend builds |
This is the number most people get wrong. A 100 Ah AGM battery only safely provides about 50 Ah of usable power, because draining lead-acid below ~50% damages it. A 100 Ah LiFePO4 battery provides close to the full 100 Ah. So lithium gives you roughly twice the usable power for the same rated size.
That is why comparing amp-hours alone is misleading: on paper an AGM looks similar, but in real use lithium delivers far more usable energy over its life.
LiFePO4 costs more upfront. But because it lasts many more cycles and gives you more usable capacity, its cost per useful cycle is almost always lower for a van that is used regularly. AGM makes sense mainly for a low-budget, low-use weekend build.
If you plan to live in your van, work remotely, or use it the whole year, choose LiFePO4. It is lighter, safer, longer-lasting and gives you more usable power. Choose AGM only if you are on a tight budget, use the van lightly, and understand you are trading upfront cost for a shorter life and less usable capacity.