Various door locks and their methods of operation are described. In one embodiment, one or more capacitors are discharged to power one or more electrical loads of a door lock and then charged by one or more associated power sources. During this type of operation, a voltage of the one or more capacitors may cyclically vary between a first voltage threshold and a second voltage threshold. Methods related to estimating an amount of energy provided to the one or more capacitors using time measurements are also described.