NiMH rechargeable batteries are made out of nickel and metal-hydride. NiMH are one type of rechargeable battery, and they are available in AAA, AA, C, D and 9-volt sizes. You can buy chargers that will recharge these batteries. Some chargers will only fit size C and D or AA and AAA while some are built specifically for 9-volt batteries. It is important to have a charger specified for your type of batteries to avoid causing the batteries to malfunction. Purchase NiMH batteries and chargers online or wherever electronics are sold.
Place the batteries into the charger with the polarities on the correct sides of the charger.
Unfold the outlet plug in the back of the charger if necessary.
Plug the charger into the outlet. This outlet can be in a wall, power strip or extension cord.
Verify that a red light is showing on the charger. The light indicates that the batteries are in the charger correctly and that they are charging.
Remove the batteries when the red light turns green. Use and recharge as needed.
Do not try to charge two different types of batteries, such as NiMH and NiCd, in the same charger. Doing this will damage the batteries and they may never hold a charge again.