A method of powering an intermittent-duty cycle winch is disclosed. The method includes identifying a number of amp-hours required to power the winch through one duty cycle, identifying a minimum required rest period between two consecutive duty cycles, and assembling a power supply unit that powers the winch based, at least in part, on the duty cycle and the rest period. The duty cycle is mechanically or thermally limited. The power supply unit includes at least two components: a power storage unit and a charging unit that recharges the power storage unit during the rest periods. The power storage unit powers the winch through at least one duty cycle. The charging unit recharges the power storage unit during the rest period so that the power storage can power the winch through at least a second duty cycle that immediately follows the end of the minimum required rest period.