C-Rate

What it means

A C-rate normalises current against capacity. 1C is the current that would fully discharge the pack in one hour; 0.5C would take two hours; 2C would take half an hour. Because it is a ratio rather than an absolute figure, it lets you compare stress on packs of different sizes.

The arithmetic is simple. On a 48V 20Ah pack, 1C is 20A. On a 48V 40Ah pack, 1C is 40A. Both are working equally hard relative to their capacity even though one is drawing twice the current.

Why it matters when sourcing

Cell datasheets state continuous and peak discharge in C, and cell selection follows from the C-rate your application demands. A commuter bike that pulls 15A from a 20Ah pack is running at 0.75C — comfortable for standard energy cells. A cargo bike pulling 40A from the same pack is at 2C, which needs higher-drain cells and usually a higher parallel count.

Sustained high C-rates cost you in two ways: cells run hotter, which accelerates capacity fade, and voltage drops further under load, which shows up as voltage sag.

Send amps, not C-rates

Do not send us a C-rate. Send the actual continuous and peak current your controller draws, in amps, and the capacity you want. We convert to C-rate against candidate cells and tell you which ones have the headroom.

The reason for that order matters: a C-rate quoted without a capacity is unanchored, and buyers frequently quote a figure inherited from a different pack size. Amps and amp-hours are unambiguous. Charge rates follow the same convention — a 20Ah pack charged at 4A is charging at 0.2C, which is the gentle end and is why higher-current chargers shorten charge time at some cost to long-term cycle life.