You may wonder why some flashlights drain batteries even when they are switched off and not in use. The batteries left inside the flashlights slowly lose charge, because of what is known as parasitic drain. And It’s important to know if the flashlights can store for months/years with batteries, or the batteries may be empty when the light is needed. Most LED flashlights need a constant power supply in order to detect when it is being turned on. This constant power is what leads to parasitic drain. A general rule for detecting flashlights with standby power drain is to look after the switch, if it’s a non-locking switch, the light has a microprocessor that is always powered to control the power and for some lights they also need a running boost converter to power the microprocessor, which will increase the drain. To prevent parasitic drain, one of the best ways is to remove the batteries from the flashlights when storing the flashlights for an extended period of time. Regardless of the power consumption, it’s always best to remove your batteries from the flashlights, which will completely stop this drain on the battery power, no matter of they are electronic switches or mechanical switches.