The Duracell MN21 battery is an alkaline battery that provides long lasting, dependable enrgy and it even manages to retain that for up to seven years in storage. There are many devices for which this battery can be used. It is commonly known to be used to power car alarm key fobs and security systems. The Duracell brand is renowned for quality, reliability and long lasting batteries. An ideal power source for the devices that require a dependable source of power.