Battery Cell Heat Calculator | BatteryPackCalc

How to Use the Cell Heat Calculator

Enter the current flowing through a single cell, that cell's internal resistance in milliohms, and your series (S) and parallel (P) counts. Heat generation follows Joule's law, q = I² × R: with the default 10 A per cell through 20 mΩ, each cell dissipates 10² × 0.02 = 2 W. The pack total simply multiplies that by the number of cells in the layout — a 13S4P pack contains 52 cells, so it sheds 104 W in this example.

The temperature-rise estimate multiplies per-cell heat by a cell-to-ambient thermal resistance. Because that value depends heavily on how the pack is built, the calculator reports a band of 3 to 8 °C/W around a 5.5 °C/W midpoint: 3 °C/W corresponds to a well-ventilated pack, 8 °C/W to an enclosed build with poor convection. For the 2 W example cell this gives a mid estimate of 11 °C above ambient, inside a 6–16 °C spread.

Note that the current input here is per cell, not per pack: parallel groups share the load, so a 40 A pack draw split across four parallel cells is 10 A each. Because heating scales with the square of current, doubling the per-cell current quadruples the heat — and conversely, doubling the parallel count at the same pack current cuts each cell's heat to a quarter. Internal resistance also varies with age, temperature, and chemistry, so a measured value gives a far better estimate than a generic one.