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The C-rate expresses charge or discharge current relative to the battery's capacity. A rate of 1C means the battery is charged or discharged in one hour: the current equals the amp-hour rating. 0.5C takes two hours (half the current); 2C takes half an hour (double the current). So the current is I = C × Capacity, and the ideal time is 1/C hours.
| Quantity | Formula |
|---|---|
| Current from C-rate | I = C × Capacity(Ah) |
| C-rate from current | C = I / Capacity(Ah) |
| Time (hours) | t = 1 / C = Capacity / I |
C-rate governs how hard you can push a battery. High rates raise internal heating (I²R loss) and, in lead-acid, reduce the delivered capacity (Peukert effect). Manufacturers specify maximum continuous and pulse C-rates — exceeding them shortens life or triggers protection.
The C-rate is the charge or discharge current expressed as a multiple of the battery capacity. 1C fully charges or discharges the battery in one hour; the current in amps equals the amp-hour rating.
Multiply the C-rate by the capacity in amp-hours: I = C × Ah. A 100 Ah battery at 0.5C draws 50 A.
Divide the current by the capacity: C = I / Ah. A 100 Ah battery at 25 A is running at 0.25C.
The ideal time is 1/C hours. So 0.5C takes 2 hours, 1C takes 1 hour, and 2C takes 30 minutes — before accounting for taper (CV) charging at the end.
It depends on chemistry. Many lithium batteries accept 0.5–1C, LiFePO4 often 0.3–1C, and lead-acid typically 0.1–0.3C. Always follow the manufacturer's maximum charge C-rate.
In lead-acid, yes — the Peukert effect means high discharge rates deliver less amp-hours. Lithium is far less affected but still loses a little capacity and generates more heat at high C-rates.
It means charging at two or three times the 1C current, filling the battery in about 30 or 20 minutes. Only cells designed for it can handle these rates without excessive heat or degradation.
Power lost as heat equals I²×R (the internal resistance). Doubling the current quadruples the heating, so high C-rates need good thermal management to stay within safe temperatures.
The definition is the same, but the safe limits usually differ. Batteries often tolerate higher discharge C-rates than charge C-rates, and manufacturers list separate continuous and pulse ratings.
Power equals current times voltage, so a higher C-rate delivers more power. A 48 V 100 Ah pack at 1C (100 A) delivers about 4.8 kW.
Continuous C-rate is the sustained current the battery can handle; pulse C-rate is a higher current allowed only for short bursts (seconds). Data sheets specify both.
Yes. Repeated high-rate charging and discharging generates heat and stress that accelerate ageing, so operating at moderate C-rates generally extends the number of usable cycles.
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