For anyone wanting to know what's inside (to potentially change the 21700 battery), I use a TORX T5 and got three of the four screws out. The other screwhead stripped even though I was applying pretty good pressure. The screws themselves are about 5.5-5.8mm long, 2mm in diameter, with a 2.8mm or so head. I don't think I compromised the waterproofness of the body as the stripped screw never seemed to move. The other three screws came out fine.
