How many amps should I charge my battery at?
Charging current is given as a fraction of capacity, called the C-rate. Battery University says lead-acid makers recommend about 0.3C, so a 100 Ah lead-acid battery takes up to 30 A, and 10 A (0.1C) is a gentle overnight rate. Lithium energy cells are charged at 0.5C to 1C, with 0.8C or less recommended for long life (BU-409).
Your battery's spec sheet wins over any rule. The calculator shows a range and the charging time each end gives, using the charging time calculator's math.
charging current (A) = battery Ah x C-rate
Charging current by battery size
Gentle and upper rates for lead-acid (0.1C to 0.3C) and lithium (0.2C to 0.5C).
| Battery | Lead-acid | Lithium |
|---|---|---|
| 20 Ah | 2 to 6 A | 4 to 10 A |
| 50 Ah | 5 to 15 A | 10 to 25 A |
| 100 Ah | 10 to 30 A | 20 to 50 A |
| 200 Ah | 20 to 60 A | 40 to 100 A |
| 300 Ah | 30 to 90 A | 60 to 150 A |