Heavy duty rechargeable battery keeps your Power Pet Door working while keeping you worry-free. If you experience a power outage, you can rest assured that your pet can still come and go as he pleases. Just snap it into the battery compartment and your Power Pet door will remain functioning in the case of a power outage The backup battery automatically recharges when the Power Pet door is powered by its AC wall adapter. When used with the optional battery charger kit (CRG-12V), sold separately, it operates the Power Pet door without the need of an AC wall connection. Simply keep one backup battery on the charger, while the 2nd battery is operating the Power Pet door. Operates the Power Pet door for approximately 1000 cycles.