Battery C-Rating Calculator | BatteryPackCalc

How to Use the C-Rating Calculator

Enter the continuous C-rating printed on the cell datasheet, the single-cell capacity in amp-hours, and your series (S) and parallel (P) counts; the pack nominal voltage is derived automatically from S × the preset cell voltage, though you can override it for a custom build. C-rating is a multiple of capacity, so the maximum cell current is C-rating × cell capacity. With the default 5C rating on a 3.5 Ah cell, each cell can deliver 5 × 3.5 = 17.5 A continuously, and that figure is the foundation for every other number the tool reports.

Pack current scales with the parallel groups, because each parallel cell shares the load: maximum pack current is P × maximum cell current. For the default 13S4P layout that is 4 × 17.5 = 70 A. Maximum power then follows from pack nominal voltage × pack current — a 48.1 V nominal pack pushing 70 A is capable of 48.1 × 70 ≈ 3,367 W. The calculator also reports how long the pack would last at that rate: discharge time in hours is 1 ÷ C-rating, so a 5C draw empties the pack in 0.2 hours, which is 60 ÷ 5 = 12 minutes.

These are absolute ceilings, not operating targets. Sustained discharge near the rated C generates heat (see the Cell Heat calculator) and accelerates aging, so design your continuous load at least 20 percent below the rated limit and reserve the full C-rating for short bursts. Note the difference between continuous and peak ratings on the datasheet — a cell rated 5C continuous may allow 10C for a few seconds — and remember that real capacity falls in the cold and as cells age, which lowers the actual current a tired pack can supply below the datasheet promise.