Three questions about using rechargeables in a surefire
1- I know blf isn’t usually a fan of Surefire stuff, but a free light is a free light. My girlfriend was given a yellow nitrolon g2 with a KX4 led head on it, but it sits unused because of the batteries. It looks like two 4.2v li-ion 16340s should be safe with it, but can anyone confirm it for sure? I’d sure hate to burn out a $60 head!
2- Does anyone have any suggestions on which cells to get? Li-ion or lifepo4? I’ve done a bit of research and have yet to come to any solid conclusions. I heard great things about the solarforce 16340s, but they are no longer for sale on their site. I saw them a while back, but hesitated to buy them and I haven’t seen them since. I’d prefer something relatively cheap, otherwise I’ll just buy a few sets of primary CR123s and call it quits and give her my jetbeam BA10.
Are there any laptop packs that use 16340s? 
3- If I buy 4.2v li-ions I’ll probably end up using my i4 to charge them for now, but if I get lifepo4 I’ll need something else. I’m thinking the xtar mp2. I like the small size and the ability to charge from USB is a major plus. At about $13 it seems great, but I’ve heard mixed reviews about its cc/cv algorithm.
What do the great mind here think?