"How long will it last?" is the question every off-grid RVer asks first. The honest answer is "it depends on your load" — but with your daily amp-hour draw and a capacity number, the estimate is straightforward. Here's the math and the real-world tables.
The short answer
A 100Ah lithium battery powers light loads (LED lights, phone charging, a 12V fridge) for roughly 1.5–2 days between charges. Step up to a 314Ah bank and you're looking at 4–6 days of the same load. Heavy draws — an inverter microwave, a water heater, or an air conditioner — can drain even a big bank in hours.
The runtime formula
Runtime (hours) ≈ Usable Ah ÷ Load (A)
- Usable Ah: lithium ≈ 95–100% of rated; AGM ≈ 50% (don't go below 50% or you'll kill it).
- Load (A): total amps drawn at 12V. A 60W device at 12V is ~5A. Sum everything running at once, then average over the day.
Worked example: 90Ah usable (100Ah lithium) ÷ 4A average load = 22 hours of runtime. That's about 1.8 days allowing for the fridge cycling.
Capacity comparison (light off-grid load ≈ 4A avg)
| Battery | Usable Ah | Runtime @ 4A | Runtime @ 8A |
|---|---|---|---|
| 100Ah LiFePO4 | ~95Ah | ~24h (1 day) | ~12h |
| 200Ah LiFePO4 | ~190Ah | ~48h (2 days) | ~24h |
| 314Ah LiFePO4 | ~300Ah | ~75h (3 days) | ~38h |
| 100Ah AGM | ~50Ah | ~12h | ~6h |
These assume a compressor fridge, LED lighting, water pump, and device charging. Add an inverter microwave (≈150A) for 10 minutes and you've burned ~25Ah in one go.
What eats the power fastest
- Air conditioner: 1,000–1,500W through an inverter ≈ 80–130A — a 100Ah bank lasts under an hour. See our A/C-on-battery guide.
- Induction cooktop / microwave: huge, short spikes; budget per use, not per hour.
- 12V fridge: the steady background draw everything else stacks on top of.
- Inverter overhead: even idle, a big inverter can pull 0.5–1A. Turn it off when not needed.
Lithium vs AGM: same label, very different runtime
A 100Ah lithium and a 100Ah AGM look identical on the shelf, but usable capacity is what matters. The AGM forces you to stop at 50%, so you only get ~50Ah — about half the real runtime. Lithium lets you use nearly all of it. For boondocking, that's the difference between "charge every day" and "charge every other day." Our full comparison breaks down the lifetime cost too.
Cold weather shortens it
Below freezing, a lithium battery's available capacity drops and — on non-heated models — charging is disabled to protect the cells. An AGM also loses capacity in the cold. If you camp in winter, size up or pick a low-temperature model. See our cold-weather storage guide and the cold-weather battery guide.
Batteries we recommend
314Ah LiFePO4 — best for multi-day boondocking
Full lineups:
Visit HumsiENK Store Visit Wattcycle Store
Frequently asked questions
How long will a 100Ah RV battery run a fridge?
A 12V compressor fridge draws roughly 40–60Ah/day. From a 100Ah lithium (≈90Ah usable) you get about 1.5–2 days before needing a charge; an AGM only gives ~50Ah usable, so closer to one day.
Does a lithium battery really last longer off-grid than AGM?
For the same rated Ah, yes — lithium gives ~95–100% usable capacity versus ~50% for AGM, and it holds voltage under load better, so your inverter and fridge behave. You effectively get roughly double the runtime from the same label capacity.
Can I run my RV air conditioner on battery?
Technically yes with a large lithium bank and a 2,000W+ inverter, but runtime is short — plan for a big bank and solar, or a generator for A/C. See the dedicated A/C guide for the numbers.
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