The sensor locker lock is powered by 4pcs AA Batteries, last 5-10 months normally. If low Voltage (<4.8V),  there will be alarm sound to remind you changing battery. All locks we supply have an external power port on it.  If battery totally exhausted, connect a battery case with 4 pcs AA battery, then unlock.  You don't have to destroy the locker/cabinet if battery dead. You can also use a  transformer to transform your city power (AC) to DC (6V) to supply power to all locks centrally.