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 .