How long does a 100Ah lithium battery last in an RV?

A 12 V 100 Ah LiFePO4 battery stores about 1,200 Wh on paper. RVWatt plans on using 80% of it, about 960 Wh, before recharging. How long that lasts depends entirely on what you run, from more than two days for a small fridge to under ten hours for a motorhome with a microwave and a CPAP.

The simple formula

Runtime in days = usable watt-hours ÷ daily watt-hours. For a 100 Ah LiFePO4 battery that is 100 Ah × 12 V × 0.8 = 960 Wh. For a 100 Ah AGM battery the calculator uses 50%, so 600 Wh. For appliances on the inverter, divide their watts by the 90% inverter efficiency, and count the inverter’s own idle draw (10 W by default) for as long as it is on.

Many LiFePO4 batteries can deliver close to their full rating. Planning on 80% leaves a reserve for cold mornings, battery aging and the gap between a battery monitor’s estimate and reality, and it matches how the calculator sizes every bank.

How long common loads last on one 100 Ah battery

Daily figures come from the RVWatt appliance library and presets. Runtimes assume no charging at all: no solar, no driving, no shore power.

What you run	Wh per day	100 Ah LiFePO4 (960 Wh)	100 Ah AGM (600 Wh)
CPAP, 40 W allowance for 8 hours (12 V)	320 Wh	3.0 days (72 h)	1.9 days (45 h)
50–65 L 12 V compressor fridge	432 Wh	2.2 days (53 h)	1.4 days (33 h)
Laptop, 6 hours on the inverter (plus idle)	493 Wh	1.9 days (47 h)	1.2 days (29 h)
8–10 cu ft 12 V RV fridge	660 Wh	1.5 days (35 h)	0.9 days (22 h)
Weekender van preset (fridge, fan, lights, pump, phones)	830 Wh	1.2 days (28 h)	0.7 days (17 h)
Starlink Standard, 8 hours on the inverter (plus idle)	880 Wh	1.1 days (26 h)	0.7 days (16 h)
Residential 120 V fridge (plus 24 h of inverter idle)	1,640 Wh	0.6 days (14 h)	0.4 days (9 h)
Full-time van preset	2,103 Wh	0.5 days (11 h)	0.3 days (7 h)
Class C motorhome preset	2,542 Wh	0.4 days (9 h)	0.2 days (6 h)

Two 100 Ah batteries in parallel double every runtime in the table. Two in series for a 24 V system store the same energy as two in parallel, so runtime in hours is the same; only the current changes.

Check the weekender van on one 100 Ah battery Just the 12 V fridge

Big 120 V appliances: the limit is current, not capacity

A microwave, kettle, induction cooktop or air conditioner can drain a small bank quickly, but the first problem is usually current. On a 12 V system, a 1,500 W microwave pulls about 1,500 ÷ (12 V × 0.9) ≈ 139 A from the battery, more at low voltage. A 1,300 W roof air conditioner pulls about 120 A, and an 1,800 W induction burner about 167 A.

Many 100 Ah LiFePO4 batteries have a battery management system (BMS) rated around 100 A continuous; the calculator uses the same 1C rule of thumb. Above that, the BMS shuts the battery off to protect it, even when it is full. AGM is more limited still: the calculator treats about 0.2C (20 A per 100 Ah) as comfortable. So a single 100 Ah battery is a fine match for a fridge, lights, fans, a CPAP and device charging, and a poor match for anything that heats or cools with electricity. Check your battery’s datasheet for its continuous and surge ratings, and see what size inverter for an RV for how inverter current, fuses and cable are sized.

How much solar keeps it topped up

Runtime only matters until the next charge. The calculator sizes solar to replace one day of use in the weakest month you travel: solar watts = daily watt-hours ÷ (peak sun hours × 0.757). For the 830 Wh weekender van in Denver from May to October (3.98 sun hours in October) that is about 276 W, so two 200 W panels. With that much solar, a 100 Ah battery mostly has to carry you overnight and through a cloudy day, not for days on end. The calculator still recommends about 173 Ah for that van, because its default is two days without charging.

If you are deciding between one battery and two, start with your own daily watt-hours from the appliance wattage chart, then compare chemistries in LiFePO4 vs AGM. For the solar side of the same question, see how much solar to charge a 200 Ah battery.

Cold weather and safety

LiFePO4 batteries deliver less capacity in the cold and most must not be charged below 0 °C (32 °F); the calculator does not model cold capacity loss, so leave margin for winter. Fuse the positive cable close to the battery with a fuse rated for the battery’s short-circuit current (often a Class T for lithium), and size the cable for the fuse. If you are not confident, have a qualified RV or marine electrician check the installation.

Work out your own runtime in the calculator

Frequently asked questions

How long will a 100Ah lithium battery run a 12V fridge?

About two days for a 50–65 L compressor fridge using 432 Wh a day, if nothing else is running and there is no charging. RVWatt plans on 960 Wh usable from a 12 V 100 Ah LiFePO4 battery, so 960 ÷ 432 ≈ 2.2 days. A larger 8–10 cu ft 12 V RV fridge at 660 Wh a day lasts about 1.5 days. Hot weather shortens both.

Can a 100Ah lithium battery run a microwave?

Often not, even when it is full. A 1,500 W microwave pulls about 139 A from a 12 V battery through an inverter, and many 100 Ah batteries have a BMS rated around 100 A continuous, so the battery shuts off. Two or more batteries in parallel, or a battery with a higher discharge rating, is the usual answer. Check your battery’s datasheet.

Why does RVWatt use 960 Wh and not 1,200 Wh for a 100Ah battery?

Because it plans on using 80% of a LiFePO4 battery’s rated capacity. Many lithium batteries can deliver close to 100%, but the 80% figure leaves a reserve for cold mornings, aging and battery-monitor error. For AGM the calculator plans on 50%, or 600 Wh from a 100 Ah battery.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.