I am using 10 1.2v NiMH batteries to power a LED module. There is a boost converter to obtain the voltage required for the LED, which is 17 v. The batteries are rechargeable so I put a charging plug into the side of the handle. To turn on and off the flashlight, is a small red button near the top of the handle. The button has an LED built inside and is used to indicate when the battery is low and to indicate when the charge is done.