it "needs" a minimum voltage to work because of the microprocessor inside that sorts out all of the digital bits - the processor will reboot if the voltage gets below a minimum point, because there are no guarantees it will continue to work properly below that voltage, so it starts back up in a known condition.

The voltage doesn't have to stay below that minimum point for very long to trigger a re-boot, so a dirty or intermittent switch or connector can cause it, even if your battery is overkill for the application - use good switches and keep connectors clean, too.