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.