When testing devices I wanted to quantify some of the battery and power issues. Some devices have low power indicators and others simply stop working when the power reaches a low level.
This is the voltage level that activates the low power indicator on a device. Not all devices have a low power indicator. If you are planning an outing and need your device to operate you can check the battery power levels to get an idea of how the device will perform. If the batteries are near the low power level then you should consider charging or replacing those batteries.
This is the point at which the device fails to operate. Some devices, such as flashflights, have no low power warning. For these devices I leave then ON until they fail. I then remove the batteries and measure the battery voltage. If you want to make sure that your device will operate you can remove the battery, check the voltage, and charge or replace the battery if the voltage level is near the power fail level.