A rechargeable battery, also known as a storage battery, is a group of two or more secondary cells. These batteries can be restored to full charge by the application of electrical energy. In other words, they are electrochemical cells in which the electrochemical reaction that releases energy is readily reversible. Rechargeable electrochemical cells are therefore a type of accumulator. They come in many different designs using different chemicals. Commonly used secondary cell chemistries are lead and sulfuric acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer).

Rechargeable batteries can offer economic and environmental benefits when used instead of one-time-use disposable batteries. Most rechargeable battery technology has been adapted into the standard “AA,” “AAA,” “C,” “sub-C,” “D,” and “9-volt” configurations that consumers are familiar with. While the rechargeable versions of these types of cells have a higher up-front cost than disposable batteries, rechargeable batteries can be discharged and recharged many times. Similarly, while the metals and chemicals in rechargeable cells can be more toxic than those in disposeable batteries, disposeable batteries nevertheless do release toxins into landfills and other more sensitive parts of the environment. Some manufacturers of NiMH type rechargeable batteries claim a lifespan up to 3000 charge cycles for their batteries.

Unlike nonrechargeable batteries (primary cells), secondary cells must be charged before use. Attempting to recharge nonrechargeable batteries is not advised as it has a small chance of causing a battery explosion.

Some types of rechargeable batteries are susceptible to damage due to reverse charging if they are fully discharged; other types need to be fully discharged occasionally in order to maintain the capacity for deep discharge. Fully integrated battery chargers that optimize the charging current are available.

Rechargeable batteries currently are used for lower power applications such as automobile starters, portable consumer devices, tools, and uninterruptible power supplies. Emerging applications in hybrid vehicles and electric vehicles are driving the technology to improve cost, reduce weight, and increase lifetime. Future applications are proposed to use rechargeable batteries for load leveling, where they would store baseline electric power for use during peak load periods, and for renewable energy uses, such as storing power generated from photovoltaic arrays during the day to be used at night.