Originally Posted by
gheezbiker
Stay away from the cheap Chinese knockoff 18650s which advertise impossible capacities. There's no such thing as a 4000 mAH 18650, but you'll find some batteries advertised that way, which often barely provide 10% of their rated capacity. Stick to the better brands.
These flashlights can make wonderful bike lights, and can serve as good flashlights for camping or other purposes when off the bike.
There may be reasons to stay away from the Chinese batteries but you are wrong about the capacity. 18650 Li ion batteries are readily avaliable in capacities of up to 2.8 Ah. Placed in a 2 serial/2 parallel battery pack, you end up with a 7.4 volt pack with a 5.6 Ah capacity.
As an owner of several 2s/2p battery packs and a long time light user, I can tell you that claiming the battery packs to provide only 10% of their rated capacity is incorrect. Ten percent of the capacity of a 5.6 Ah pack would be only 0.6 Ah which wouldn't power any kind of light for more than a few minutes.