Complete noob here I am currently running my lights on cr123a batteries and wanted to know if I get rechargeable batteries which ones would be best and if my old charger that I use to use for my rc cars would work for charging them. I am sure you guys need more information from me to give me a better answer but at the moment I am so new to this that I do not know where to start
IMHO best bang for the buck are the Trustfire Flames , your charger should work but don't charge then with more than 0.4 - 0.5 Amps , or just buy a good cheap Trustfire Charger ;)
Well first of all 18650s will not fit into your surefire g2. Also you may or may not be able to use 2 rcr123as. If it is incandescent then no, however a p90 would allow it to work.
But if it is the g2x or the g2 led then 2 rcr123a's should work, however I would recommend using some lifepo4 batteries since they are 3.2 volts instead of 3.7. Your charger however will not be able to charge the lifepo4 batteries so you would need a different one. I currently use http://www.batteryjunction.com/4parc390reli.html, but surefire recently came out with their own version http://www.surefire.com/batteries/sf2r-kit01-charger-kit.html.