Two 100 Ah LiFePO4 batteries is the answer for most vans. Here's the math that says whether your build is "most vans."
Ah = (Wh/day × days × 1.25) ÷ 12 ÷ 0.80
LiFePO4 at 12V assumed — 95% of vans. Days = autonomy before recharging (1 day if you drive or solar daily, 2 if you park in shade).
Everything hinges on the honest watt-hour audit. Van loads are small individually and relentless collectively: the fridge never turns off, and it's the anchor of every load list.
With 1 day of autonomy (you drive or solar-refill daily): (1,160 × 1 × 1.25) ÷ 12 ÷ 0.80 = ~150 Ah → two 100 Ah batteries, comfortable. With 2 shaded days parked: ~300 Ah → three or four.
(3,000 × 1 × 1.25) ÷ 12 ÷ 0.80 = ~315 Ah at 12V → three to four 100 Ah batteries, and at this point a 48V bank starts making sense: 80 Ah at 48V does the same job with thinner cable and cooler runs. Induction is the fork in the road — propane cooking keeps the whole build one battery size smaller.
| Build | Daily use | Ah needed | Typical hardware | Cost* |
|---|---|---|---|---|
| Bare weekend | 0.8 kWh | 85 Ah | 1 × 100 Ah | $250–400 |
| Weekend/light | 1.5 kWh | 160 Ah | 2 × 100 Ah | $500–800 |
| Full-timer | 3.0 kWh | 315 Ah | 3–4 × 100 Ah | $1,400–2,200 |
| Full-timer + AC (4 h) | 5.5 kWh | 575 Ah | 6+ × 100 Ah or 48V | $2,600–4,000 |
*Q3 2026 LiFePO4 street prices. Rooftop AC is why some vans quietly go 48V: 5.5 kWh/day at 48V is ~145 Ah, not 575.
The 1.25 covers inverter conversion losses (5–10%), wiring loss, and the fact that LiFePO4 capacity ratings are optimistic below freezing. The 0.80 is the usable fraction — LiFePO4 tolerates deep discharge, but every percent below 80% DoD shortens cycle life disproportionately, and BMS low-voltage cutoffs will strand you before "100% of rated Ah" is actually delivered anyway. Skipping either factor is how people end up one battery short and blaming the brand.
The 100 Ah LiFePO4 drop-in is the van standard — buy in twos so you can parallel later — and a 2,000W pure-sine inverter covers everything except induction at full boil.
100 Ah LiFePO4 on Amazon → 2,000W inverters on Amazon → 12V fridges on Amazon →
The battery count only matters if you can refill. Three realistic sources, sized against the same daily figure:
More sizing: the battery bank sizer directory, the cabin-specific version in what size battery bank for an off-grid cabin, and the charging side at GeneratorSizer ↗ / SolarSizer ↗.
More sizing: the battery bank sizer directory, the cabin-specific version in what size battery bank for an off-grid cabin, and the charging side at GeneratorSizer ↗ / SolarSizer ↗.
A light weekend build (1.5 kWh/day: fridge, lights, fan, phones) needs about 160 Ah at 12V LiFePO4 — typically two 100 Ah batteries. A full-timer build (3 kWh/day) needs ~315 Ah at 12V, commonly three to four 100 Ah units.
For minimal weekend use — 12V fridge, LED lights, phone charging, a fan (about 700–800 Wh/day) — one 100 Ah LiFePO4 works with a 1.25-day reserve. Add induction cooking, a diesel heater on full, or a work day of laptops and 100 Ah runs out by evening; two 100 Ah batteries is the common real-world answer.
Yes. A typical 12V compressor fridge draws 40–60 W at 30–40% duty cycle — roughly 400–500 Wh per day, about 250 Wh overnight. That is under 30% of a 100 Ah (1,280 Wh) battery, so overnight is easy; the rest of the load list decides the real count.
Vans almost always stay 12V because DC appliances are 12V-native and loads stay under 2 kWh/day. Above roughly 3 kWh/day with a big inverter (induction cooking, AC), 24V halves the current and wire gauge; 48V only pays off in large stationary systems, not vans.
About two days by itself: the fridge's ~400–500 Wh/day against 1,024 Wh usable (100 Ah LiFePO4 at 80% DoD). Real vans never run the fridge alone, which is why the full load list — not the fridge — sets the battery count.
Full-time off-grid instead of van life? The same formula at what size battery bank for an off-grid cabin covers cabin-scale autonomy math, and the battery bank size calculator directory maps daily use to Amp-hours at every voltage.