How Long Will a 100Ah Battery Last? (Real Van Life Examples)
By Frank Zale · July 14, 2026 · 5 min read
A 100Ah battery is the single most common battery size in camper vans, and the most common question about it is simple: how long will it actually last? The short answer: a 100Ah LiFePO4 battery holds about 1,024 usable watt-hours, which runs a 12V fridge for roughly two days, a diesel heater for four to five nights, or an induction cooktop for about 37 minutes. The long answer depends on what you plug in — so here are the real numbers.
The math behind every runtime estimate
Battery runtime always comes down to one formula:
Runtime (hours) = usable watt-hours ÷ appliance watts
A 12V, 100Ah battery stores 1,280 Wh on paper (12.8V × 100Ah). But you can't use all of it:
| Battery type | Rated | Safe depth of discharge | Usable energy |
|---|---|---|---|
| 100Ah LiFePO4 | 1,280 Wh | 80% | ~1,024 Wh |
| 100Ah AGM | 1,220 Wh | 50% | ~610 Wh |
That difference is why a "100Ah" AGM lasts barely half as long as a "100Ah" lithium battery. If you're still choosing between the two, our LiFePO4 vs AGM comparison covers weight, lifespan, and cost per kWh.
One more haircut: anything that runs on household AC power goes through an inverter, which wastes about 10% of the energy. So for AC appliances, multiply your usable energy by 0.9.
Real runtimes for common van appliances
All numbers below assume a 100Ah LiFePO4 with 1,024 Wh usable.
| Appliance | Power draw | Runtime on 100Ah |
|---|---|---|
| 12V compressor fridge | 45W (cycles ~50%) | ~45 hours (about 2 days) |
| Roof vent fan (medium) | 25W | ~41 hours |
| LED lights | 15W | ~68 hours |
| Diesel heater (running average) | 30W | ~34 hours |
| Starlink Standard | 50W | ~20 hours |
| Laptop charging (via inverter) | 65W | ~14 hours |
| 12V heated mattress pad | 45W | ~23 hours |
| CPAP without humidifier | 40W | ~25 hours |
| Electric kettle (via inverter) | 1,000W | ~55 minutes |
| Induction cooktop (via inverter) | 1,500W | ~37 minutes |
Two patterns worth noticing:
- DC appliances sip; AC appliances gulp. Everything that plugs into a 12V socket runs for days. Everything that needs an inverter — especially heat-producing appliances — eats the battery in minutes.
- The fridge is your baseline. It's the one load that never turns off. Budget roughly 400–540 Wh per day for a compressor fridge before you add anything else.
How long will a 100Ah battery last in a real day?
Nobody runs one appliance at a time. Here's a realistic "weekend camper" day:
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| 12V fridge | 45 (cycling) | 24 | ~420 |
| Vent fan | 25 | 6 | 150 |
| LED lights | 15 | 4 | 60 |
| Phone charging | 10 | 3 | 30 |
| Total | ~660 Wh/day |
1,024 Wh usable ÷ 660 Wh/day ≈ 1.5 days with no charging at all. Add a laptop and Starlink for remote work and you're at roughly 1,100 Wh/day — now the battery doesn't even cover one full day.
This is why a 100Ah battery works fine for weekenders with solar, and why full-timers almost always end up at 200Ah or more.
Solar changes everything
Runtime-on-paper assumes zero charging. In practice, even a modest solar array resets the clock every day. A 200W panel in decent sun makes roughly 750 Wh per day (200W × 5 sun hours × 0.75 real-world factor) — more than the entire weekend-camper load above.
The right way to think about it: your battery bridges the night and cloudy days; your solar covers the average day. Size them together, not separately. Our free van solar calculator does both at once — enter your appliances and it sizes the battery, panels, charge controller, and wiring in one pass.
How many amp-hours do you actually need?
Work backwards from your daily watt-hours:
- List every appliance, its watts, and hours per day.
- Add up the daily watt-hours.
- Multiply by the days of autonomy you want (2 is a good default).
- Divide by 1,024 to get how many 100Ah LiFePO4 batteries that takes.
A 660 Wh/day weekender needs 1,320 Wh for two days — one 100Ah battery is close, and a bit of solar closes the gap. A 1,500 Wh/day full-timer needs about 3,000 Wh — that's a 300Ah bank. The full walkthrough is in our amp-hours sizing guide.
FAQ
How long will a 100Ah battery run a fridge?
A typical 45W 12V compressor fridge cycles on and off, averaging around 20–25W. A 100Ah LiFePO4 battery runs it for roughly 40–48 hours; a 100Ah AGM manages about half that.
How long will a 100Ah battery last with an inverter?
The inverter itself only adds its idle draw (5–15W), but the AC appliances it powers are the real load. A laptop is fine (~14 hours of charging). A 1,500W induction cooktop drains the whole battery in about 37 minutes.
Is 100Ah enough for van life?
For weekend trips with a fridge, fan, lights, and phones — yes, especially with 200W of solar. For full-time living or remote work with Starlink and a laptop, 200–300Ah is the realistic range.
Can I just add a second 100Ah battery later?
With LiFePO4, yes — wire two identical batteries in parallel to double capacity. Match brand, model, and ideally age. Your charge controller and wiring may need re-checking; run your new setup through the calculator to confirm.