An accumulator is a rechargeable battery (also known as a secondary battery) or cell. Common varieties include the lead-acid accumulator and nickel-cadmium (NiCd) batteries. However, more and more environmentally-friendly batteries such as NiMH (nickel metal hydride) and NiH (nickel hydride) are also becoming available.
The term accumulator is also applied to aA component of a heat pump that stores liquid and keeps it from flooding the compressor. The accumulator takes the strain off the compressor and improves the reliability of the system.