Nickel-Metal Hydride (NiMH) batteries are rechargeable energy storage devices known for their higher energy density compared to Nickel-Cadmium (NiCd) batteries, making them suitable for a wide range of applications from consumer electronics to hybrid vehicles. They are environmentally friendlier than NiCd batteries due to the absence of toxic cadmium and have a lower self-discharge rate than traditional rechargeable batteries, although they still require proper management to prevent overcharging and overheating.