NiMH (Nickel Metal Hydride) batteries are rechargeable batteries made with a combination of nickel and metal hydride. They are typically used in applications that require long-runtimes or high power. The main advantage of the NiMH battery is the fact that it has a higher energy density than other rechargeable batteries, which means it can store more energy for its size (weight). Additionally, it does not suffer from memory effect, which means that it can be recharged from any state of charge without any loss in performance. NiMH batteries are more environmentally friendly than most other rechargeable batteries, as they contain no toxic substances, such as mercury.