In the last few years, I’ve seen the G2x on sale in the $50 range a few times. I don’t know if that’s still true right now though. While not as bright as a lot of other $50 lights, and of course a bit large with a battery compartment that is a bit small, I think it could still be considered a budget light with the right criteria. The “Pro” model just means it has a low and a high mode. It comes on first in low, then high. The “LE” model has the modes reversed, and the “Tactical” model is just high. Because it’s a constant current (and a Surefire), it’s pretty green on low.
Anyway, the Keeppower P1665J cell is a protected wrapper around the Sanyo 4.35v 16650. I don’t know if this is advisable or not, but I have therefore used a 4.35v capable charger with it. And you do gain runtime. Off the charger, the battery tends to read around 4.26-4.28v with my multimeter, not 4.35v. So I don’t know if that’s the protection circuit preventing the internal cell from reaching max capacity/voltage, but it does make a non-trivial difference in the runtime:
Obviously missing from the above is a test on primary CR123’s, but I’m not that inclined to do such a test/waste $5 in batteries. I feel Surefire tends to be pretty honest in their performance claims and I suspect their 90-minute claim is reasonable. I stopped the 4.35v test a bit too early, but it’s going over 80 minutes before dropping to 10%. I suspect CR123’s have a tad more oomph in them.