Off-Grid Battery Bank Sizing Calculator

Estimate the leisure battery capacity an all-electric van needs from your daily energy use, the days of autonomy you want, and your usable depth of discharge. The maths runs entirely in your browser — nothing you type is sent or stored.

Daily energy use (Wh/day) Days of autonomy (days) Usable depth of discharge (%) System voltage (V)

Energy to store — Wh

Battery capacity — Ah

Methodology

Battery sizing follows two deterministic steps, the standard approach used by off-grid system designers: first the energy you must store, then the capacity at your system voltage.

• Energy needed (Wh) = daily use (Wh/day) × days of autonomy ÷ (usable depth of discharge ÷ 100).
• Battery capacity (Ah) = energy needed (Wh) ÷ system voltage (V).
• LiFePO4 typically allows ~80% usable depth of discharge; lead-acid closer to 50%.
• This is a planning estimate — add margin for inverter losses, cold weather and ageing.

This calculator gives a planning estimate, not a guaranteed specification. Real-world capacity is reduced by temperature, inverter and wiring losses, charge efficiency and battery ageing. Size your charging (solar, DC-DC, mains) to match, and confirm figures against your battery and appliance datasheets before buying.