Before buying this, please consider the Nightcore Tube, 9.6 grams functional, 45 lumens, flexible functions, RECHARGEABLE, IP65 dust and water resistant, impact resistant, 1 hour runtime on High, 5 colors to choose from.
It's never (AFAIK) come on in my pocket and drained the battery. MicroUSB charging, which I have literally everywhere. I'm done with overpriced batteries, particularly ones that fit only 1 or 2 items. I'm skeptical about that 7.4g includes batteries, but even so, ~2g is a small price to pay to keep $25 in your pocket, before investing in replacement batteries.
TEC, consider designing something with similar durability, or even just build a trick housing for the Nitecore guts, which you could likely source for a few $'s. Did I mention it's rechargeable?