Hell, the battery rated voltage is 1.2 V per cell (nicad). They work fine all the way down to 1.07 Volts per cell. So I have ran packs for years using them down to 4.6 Volts without worry. Packs and airplanes that I know really well and have graphed out to even lower voltage. But I use a very good digital multimeter (Fluke) and a power resistor to load the airborne pack to about 300 mA while testing.