The most powerful rechargeable battery within the Duracell brand’s rechargeable range is the Duracell Ultra. Although the 9v sized battery is generally used in low energy consuming devices, they still need replacing and sometimes they are used in devices that are used very often which means although they are using low amounts of energy, because that low amount of energy is being used so often it will last for less than if used in a device used less often. This means it needs replacing more often-but now it can be recharged instead! Using its DuraLock technology it will even contain its energy after charge when not n use for up to one year, until your ready to use it.