The formula
Current (A) = C-rate × Capacity (Ah)
C-rate = Current (A) ÷ Capacity (Ah)
Time (h) ≈ 1 ÷ C-rate
Typical limits
| Battery | Recommended charge | Continuous discharge |
|---|---|---|
| Flooded lead-acid | 0.1–0.2C | Best below 0.2C |
| AGM | 0.2–0.3C | Up to about 0.5C |
| LiFePO4 leisure battery | 0.2–0.5C (some 1C) | 0.5–1C, set by the BMS |
| LiPo (RC/drone) | 1C unless rated higher | As marked, e.g. 25C–100C |
These are typical figures. Always use the limits on your battery's datasheet, which for lithium batteries are set by its BMS.
Frequently asked questions
What does 0.5C mean?
It means a current equal to half the battery's amp-hour capacity: 50 A for a 100 Ah battery, which would charge or discharge it in about two hours.
What size charger for a 100Ah battery?
For lead-acid, around 10–20 A (0.1–0.2C). For LiFePO4, 20–50 A is common, within the battery's maximum charge current.