Battery Series and Parallel Connection Calculator

What do series and parallel connections change?

Connecting cells or batteries in series adds their voltages while capacity (Ah) stays the same. Connecting them in parallel adds their capacities while voltage stays the same. Energy (Wh) scales with the number of cells either way.

• Voltage: V = S × cell voltage
• Capacity: C = P × cell capacity
• Energy: E = V × C

S is the series count and P the parallel count. Packs are often written like 4S2P: four in series, two in parallel, eight cells in total.

Example

A 4S2P pack of 3.7 V 2.5 Ah cells: voltage 4 × 3.7 = 14.8 V, capacity 2 × 2.5 = 5 Ah, energy 14.8 × 5 = 74 Wh.

Two 12 V 100 Ah batteries in series make 24 V 100 Ah, in parallel 12 V 200 Ah. The energy is 2400 Wh in both cases.

Layout from a target

Divide the target voltage by the cell voltage and take the nearest whole number as the series count. Divide the target capacity by the cell capacity and round up. For 48 V 20 Ah with 3.2 V 6 Ah cells you need 15 in series and 4 in parallel, 60 cells in total. The resulting pack is 48 V 24 Ah.

Things to watch

Nominal voltage is an average: a full pack sits higher and an empty pack lower. The connected device must tolerate both ends. Use only cells of the same type, capacity and age together. Equalise voltages before connecting in parallel. Never run a lithium pack without a protection circuit.