Sizing & runtime

Battery Bank Voltage & Capacity Calculator

Get the voltage, capacity and energy of a bank made of identical batteries in series strings connected in parallel.

Voltage per battery

Capacity per battery

Batteries in series (per string)

Strings in parallel

Formula

V(bank) = S × V(battery)
Ah(bank) = P × Ah(battery)
Wh(bank) = V(bank) × Ah(bank)
N = S × P

2S2P of 12 V 100 Ah = 24 V, 200 Ah, 4,800 Wh, 4 batteries.

Use identical batteries (same model, age, capacity and state of charge) in one bank.
Series connection does NOT add CCA; parallel connection does.

Nominal capacity (Ah): Charge a battery delivers under rated conditions, usually over 20 hours (C20) at 25 °C.
Usable capacity: The part of the nominal capacity you can use without damaging the battery — about 50% for lead-acid, 80–90% for LiFePO4.
Cranking current (CCA): Current deliverable for a short time in the cold to start an engine. It measures power, not stored charge, and cannot be converted to Ah.
Stored energy (Wh): Ah × voltage. The right unit to compare batteries of different voltages.