Fast charging employs a high charging current which enables you to charge up a NiMH battery in a relatively shorter time, ranging from five hours to even half an hour.

Using a low charging current, slow charging often refers to overnight charging, which normally takes over 12 hours to charge up a NiMH battery.

However, the time it takes to fully charge a battery depends on the charging current of the charger and the capacity of the battery.

Imagine filling up a bucket under a running water tap. The bigger the bucket, the longer it takes to fill it up. You can also increase the rate of filling the bucket by turning up the tap a bit more.