RV and Trailer Calculators

RV battery runtime.

Enter the battery size, how much of it you allow yourself to use, and the average load, and get the runtime in hours and days. Runs in your browser; nothing is sent or stored.

Inputs

Battery capacity

Amp-hours of one battery, from the label or datasheet.

System voltage

Batteries in parallel

Batteries wired in parallel add amp-hours. For batteries in series, use the combined voltage and a count of 1.

Battery type (sets depth of discharge)

Presets are common rules of thumb, not published standards. Use the maker's datasheet.

Usable depth of discharge

Average load

Watts averaged over the time. A 5 A load at 12 V is 60 W.

Load runs on

Inverter efficiency

Only used for AC loads. 85 to 95 is typical; check your inverter.

Hours the load runs per day

24 for a load that never stops, like a fridge control board; less for lights or a TV.

Result

Fill the form and press Calculate.

Runtime = usable watt-hours / average load. One 12 V 200 Ah battery holds 2,400 Wh; using 50 percent leaves 1,200 Wh, which runs a 100 W AC load through a 90% efficient inverter for 10.8 hours.

Worked example

One 12 V, 200 Ah battery: 200 x 12 = 2,400 Wh. Using 50% leaves 1,200 Wh (100 Ah). A 100 W AC load through a 90% inverter draws 100 / 0.90 = 111.1 W from the battery, about 9.3 A at 12 V. Runtime: 1,200 / 111.1 = 10.8 hours.

How it works

Usable Wh = Ah x volts x batteries x depth of discharge. Hours = usable Wh / (load W / inverter efficiency). The depth-of-discharge presets (50 percent for lead-acid and AGM, 80 percent for lithium iron phosphate) are common rules of thumb. Battery University notes that a battery should not be run fully flat and that cycling at less than full discharge increases service life; the right limit for your battery is in its datasheet.

Real runtime is shorter in cold weather, with an old battery, or with a load that spikes (microwave, air conditioner). Solar and alternator charging are not counted. Wire gauge, fuses and battery safety are for a qualified installer.

Sources opened 2026-10-08: BU-501: Basics about Discharging - Battery University. Planning aid only, not professional, engineering or safety advice. Your vehicle, trailer, tire, battery and boat manuals and the weight labels on your equipment come first; when in doubt, weigh it or ask a qualified professional.

FAQ

How do I convert amp-hours to hours of runtime?

Multiply amp-hours by volts to get watt-hours, multiply by the usable share of the battery, then divide by the load in watts.

How much of an RV battery can I use?

It depends on the chemistry and the maker. Many people plan on about half of a lead-acid battery and about 80 percent of a lithium iron phosphate battery, which are rules of thumb. Check the datasheet.

Why does an inverter shorten runtime?

An inverter wastes some energy as heat, so the battery supplies more than the AC load uses. This calculator divides the load by the efficiency you enter.

Do two batteries double the runtime?

Two identical batteries in parallel double the amp-hours and so double the runtime at the same load. In series they add voltage, not amp-hours.

Does this include solar charging?

No. It shows runtime on stored energy only. Solar, shore power and the alternator add to it.