Charge on a storage capacitor in a backup power supply is managed by discharging the capacitor into an aircraft recorder that is to be powered when a primary power source fails. During the discharging, a first amount of energy discharged from the capacitor is measured along with the length of the discharge time. The first amount of energy and the discharge time are employed to define a target energy level to which the capacitor should be charged to enable the backup power supply to adequately power aircraft recorder. Then charging of the capacitor commences while a second amount of energy stored in the capacitor is measured. The capacitor charging terminates when the second amount of energy reaches the target energy level. Definition of the target energy level also may take into account variation in temperature of the capacitor.