An accumulator is an apparatus by means of which energy can be stored, such as a rechargeable battery or a hydraulic accumulator. Such devices may be electrical, fluidic or mechanical and are sometimes used to convert a small continuous power source into a short surge of energy or vice versa. Other examples of accumulators include capacitors, compulsators, steam accumulator, wave energy machines and pumped-storage hydroelectric plants.

In general usage in an electrical context the word accumulator would normally mean a lead-acid battery.