C-Rate

The C-rate expresses a charge or discharge current as a multiple of a battery's capacity. For a 100 Ah battery, 1C is 100 amps and 0.1C is 10 amps.

Battery University describes 1C as a one hour rate, 0.5C as two hours and 0.1C as ten hours. Lead acid is usually charged at 0.1C to 0.3C, which is 10 to 30 amps for a 100 Ah battery. Lithium is commonly charged at 0.2C to 0.5C, or 20 to 50 amps.

The battery charging current calculator turns C-rates into amps for any battery. The guide to lithium vs lead-acid charging explains why the two chemistries take different rates.