If you have the Philips HeartStart AED defibrillator at your home or office, this is the replacement battery for the life-saving device. The Philips HeartStart Replacement Battery is easy to install on your own and includes instructions. It features a long-life, lithium battery that lasts up to 4 years once it"s installed and the battery doesn"t require recharging. The battery has an "install by" date that"s clearly stated on the back. Once it"s installed, your battery"s 4 years begins. This quality battery arrives in a protective case.