Apparatus and method to measure energy capacity of a backup power supply without compromising power delivery

A device includes a backup power supply configured to provide power to an external system upon loss of primary system power, the backup power provided by at least one capacitor; logic to create, while the capacitor is available as the backup power supply to the external system, a transient elevation of the capacitor's stored potential above a upper predetermined operating potential of the capacitor; logic to obtain measurements of the capacitor's output voltage during the transient elevation of the capacitor's stored potential; and logic to determine a capacitance of the capacitor from the measurements; the device comprising multiple capacitors in series; logic to discharge each capacitor in series individually from the others; and logic to monitor for overcharging of any of the capacitors in series, and, during charging of the capacitors in series, to operate the discharge logic for any capacitor in the series that is in danger of overcharging.