My Son sent down 3 Home Depot special single LED lights. They are unbranded, 5 inches long and have the end switch.
I took out the triple battery holder and took 1 laptop lipo battery, cut a piece of PVC pipe and split it down the side, and slipped it over the lipo cell. I then took a freshly charged lipo cell, and did a discharge, bleeding off that 4.15 v, down to 3.9.
Doesn't take much and, the LED seems fine. At night, this light can illuminate things over 100 yards away, no problem. The end switches are junk, so, I need to figure out a switch. IF I tighten the end too far, the switch doesn't function, so, I back it off until it works OK, then run a couple wraps of vinyl tape around the joint.