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.
The London tower bridge is operated via an accumulator. The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators. In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system.