I don't know where to post this so hopefully this is ok. I just bought a Kangertech Subox Nano but now apparently I need a battery. What is the best brand/kind? I'm fairly new to this & confused on this battery thing. I know it has to be 18650 whatever that means. I just need a name/type?? of a good battery for the Nano so I can buy one on ebay. Please help! lol