Sizing & runtime

Series & Parallel Connection Calculator

Tell us the bank you need; we compute how many batteries to wire in series and in parallel.

Target bank voltage

Target bank capacity

Voltage per battery

Capacity per battery

Formula

S = V(target) ÷ V(battery)   (must be a whole number)
P = ⌈Ah(target) ÷ Ah(battery)⌉
N = S × P

24 V 300 Ah with 12 V 100 Ah batteries → S = 2, P = 3 → 6 batteries (2S3P).

Wire parallel strings with equal-length cables and take the main leads from diagonally opposite corners.

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.