Acronym for nickel metal hydride, a type of rechargeable battery. Unlike earlier rechargeable designs, such as those based on nickel-cadmium (NiCad) which quickly lost their charge, an NiMH has at least two or three times the capacity of the older design and there is very little memory effect. We recommend always using rechargeable batteries in all devices that require batteries. Never, under any circumstances, simply throw away a dead battery. Most cities have a place to drop off such hazardous materials. NiMH batteries can be recycled; older types cannot.