Re: Operating Voltage for Streamlight TLR1, Surefire X300 and 4sevens Maelstrom MMX
If it has a max of 8.4V, you are pretty safe with two LiIon cells. That 8.4 number didn't come from nowhere, and it didn't come from any of the components in the light (trust me, I work with this stuff every day). It came from someone saying "two 4.2V cells is okay". In other words the folks writing the specs are telling you that it's okay to do what you want to do. That's almost as good as a CPF member saying he's been doing it for years.
The other lights though are troublesome. Short of finding a max voltage spec like the MMX, I'd say it's a bit of a gamble. I've never (well, rarely) seen a part with a max voltage between 6.3 (max for 2 CR cells) and 8.4 (max for 2 LiIon cells), but you could run into power dissipation problems at any point. You could say "it's not a big risk, I'll try it" or you could say "it's not worth the risk, I'll stick with CRs", and you could defend either position and you'd have supporters and detractors either way.