My G/F had a rainbow Vamo we got from FT, and she got too much juice inside it and it fried. I Wanted to get her another, but maybe something a little better, so I found a 55 watt Vamo on FT, and before I read it more closely, bought it. I received it, and was at first puzzled as to why it wouldnt work with a fully charged single 18650. It reported low voltage. So I tried it with a pair of old 18350's I had and it fired up and worked normally. Well, I knew it wasnt a good idea to use old ICR batteries in thins thing, so I got me some 18350 IMR's. All well. Then I took the bottom section off the dead Vamo, and put it on the bottom of my working Vamo, and thought, I bet 2 18490's would fit in there perfectly. Sure enough, I had several IMR 18490's laying around form my ProVari. I poped them in and it works great. Kinda long, but so far seems like it would have some decent battery life @ ~20 watts.