Battery Pack Calculator

Work out what a pack of cells actually gives you. Enter the cell and how many in series and parallel to get pack voltage, capacity, energy and charge voltage.

Cell nominal voltage (V)

Cell capacity (mAh)

Cells in series (S)

Strings in parallel (P)

Cell max charge voltage (V)

Load current (mA, optional)

Pack --

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The formula

Pack voltage   = cell voltage x S
Pack capacity  = cell capacity x P
Energy (Wh)    = pack voltage x pack capacity / 1000
Charge voltage = cell max voltage x S

S = cells in series, P = strings in parallel

How it works

Series raises voltage, parallel raises capacity. A 3S2P pack of 3.7 V 2000 mAh cells is 11.1 V and 4000 mAh — six cells either way, but the arrangement decides which number you get.

Charge voltage is the one that matters for safety. Li-ion cells charge to 4.2 V each, so a 3S pack needs a charger set to 12.6 V, not 11.1 V. Getting this wrong damages cells or starts fires.

Only ever parallel cells of the same chemistry, capacity and state of charge, and use a BMS. Mismatched cells in parallel will try to equalise through each other.

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