A battery is a device that stores electrical energy. Battery converts chemical energy into electric energy. Battery is a collection of cells. Cells are the basic electrochemical units in the battery. Cells are connected either in series or parallel to form batteries. Parallel: A term used to describe the inter-connection of cells or batteries in which all like terminals are connected together. I.e positive terminal is connected with the positive terminal of another cell. Series: The inter-connection of cells or batteries whereby the positive terminal of the first is connected to the negative terminal of the second, and so on.

There are three main types of battery available in the market.  They are alkaline, nickel metal hydride (NIMH), and lithium ion.

An alkaline battery uses zinc as the negative electrode and manganese dioxide as the positive electrode. As such, alkaline batteries are single use, disposable batteries. Once discharged they cannot be safely recharged. Alkaline batteries are the cheapest on a per-unit basis.

Nickel Metal Hydride Batteries (NiMH): The negative electrode in NiMH battery is an inter metallic compound that includes nickel. The positive electrode is nickel hydroxide. These batteries are rechargeable.

Lithium ion  (Li-ion) batteries:    are the newest of the three primary types. They are rechargeable batteries commonly used in portable electronics, electrical vehicles, mobile phones etc. One of the advantages of Li-ion batteries is that they have more life (charging cycles) compared to other types of batteries.  Lithium batteries quickly recharge; usually in 1-3 hours.