A system comprises a battery and a battery-powered device. Battery contacts and a data interface are therebetween. The battery includes low-power and high-power circuits to output power, from a cell, to the battery-powered device via the contacts. The high-power circuit outputs power higher than the low-power circuit. A switch(es) connects and disconnects the high-power circuit to/from the contacts, the low-power circuit connected to the contacts when the switch disconnects the high-power circuit. A voltage detector: detects a battery-voltage on the contacts and an output voltage on the data interface; when the output voltage is greater than the battery-voltage, controls the switch to connect the high-power circuit to the contacts; and when the output voltage is below the battery-voltage, controls the switch to disconnect the high-power circuit from the contacts. The battery-powered device provides the output voltage on the data interface as powered from the contacts by the battery.