Other than chargers made specifically for proprietary batteries, there are two main types of battery chargers: NiCad and NiMH. A charger should be compatible with the type of batteries you use.
Most NiMH battery chargers also charge NiCad batteries. But the reverse is not necessarily true. Do not charge NiMH batteries in a charger designed for use with NiCads, as the NiHM batteries may not fully charge. Whichever charger you buy, make sure it is designed to prevent battery overcharging.
Types of battery chargers
Universal battery chargers
A universal battery charger charges common types of NiMH and NiCad batteries such as AA, AAA, C, D and 9 Volt. They typically charge for a fixed length of time. They are good for household use but generally not recommended for batteries used in digital cameras.
Smart battery charger
A smart battery charger, also called an intelligent charger, provides just the right amount of charge for a battery. When batteries are fully charged, the unit automatically shuts off or goes into trickle charge mode. A trickle charge keeps a battery fully charged but will not overcharge it.
Car battery charger
Plugs into the cigarette lighter of your car.