Off-Grid Solar Calculators

Battery storage

Battery Bank Sizer for RV/Van

Estimate how large a battery bank you need so an RV, van or cabin can run for a chosen number of days without sun. The result is rated capacity, not just the energy you plan to use.

Inputs

Wh

Total watt-hours you expect to use in a typical 24 hours (lights, fridge, laptop, etc.).

days

How many days you want to run with little or no solar charging.

Usable fraction of the rated bank. LiFePO4 can be used much deeper than lead-acid.

System voltage of the house battery bank.

Combined charging, wiring and inverter losses. 90% is a conservative off-grid default.

Results

Usable energy to cover
3,000Wh

Daily use multiplied by days of autonomy, before chemistry and losses.

Rated bank size
3,509Wh

Nameplate watt-hours after DoD and round-trip efficiency.

Rated capacity
292Ah

Nameplate amp-hours at the chosen system voltage.

Recommended gear

Engineering methodology

Usable energy to cover = daily watt-hours × days of autonomy. Rated watt-hours = usable energy ÷ (DoD × round-trip efficiency). Rated amp-hours = rated watt-hours ÷ battery voltage, again from Wh = Ah × V. Round-trip efficiency accounts for charge, wiring and inverter losses (often around 85–95%).

Frequently asked questions

How many days of autonomy should an RV or cabin battery bank have?

Two days is a common off-grid starting point: one day of use plus a cloudy day. Winter or heavily shaded sites often need more. This is an energy budget, not a generator or solar-array design.

Why does 12 V need more amp-hours than 48 V for the same watt-hours?

Watt-hours are energy. Amp-hours = watt-hours ÷ volts. A 2.4 kWh bank is 200 Ah at 12 V and 50 Ah at 48 V. Voltage does not change the energy you must store; it only changes the Ah number on the label.

What round-trip efficiency should I enter?

About 90% is a conservative mixed-load default. Efficient LiFePO4 DC loads can approach 95%. Inverter-heavy AC use is often closer to 85%. The factor is applied as rated Wh = (daily Wh × days) ÷ (DoD × efficiency).

More in this cluster

All battery storage tools