Li-Ion 18650 Battery: 7.3V 5.2Ah (38Wh, 9A rate, 2x2SQ, INR18650M26)

This battery pack is great and powerful. It has 4000mah capacity. The light I built uses CREE XP-E R2 which draws about 1000ma (it puts out about 200 lumens), so with this battery I can ride mountain bike at night for about 4 hours, although I usually only ride 2 hours a week. The extra capacity is nice so if I forgot to charge it after one use I still have enough juice for one more use. I'm thinking about using this battery pack to hook up to two lights, in which case it would provide enough juice for two hours. However, I am thinking about building lights with the dimming feature so I can use the low setting while climbing up the mountain to save energy and turn it on full blast when going back downhill. I estimate that this type of set up would give me about 4 hours of use with this battery, The battery is quite light in weight, or at least light enough that it can be mounted on the back of my bicycle helmet without it feeling awkward. The 18 AWG wire that came with it was more that adequate for my application and 6" wire provided enough length for connection between the battery and the light on the helmet as well as when mounted on the handle bar. I only bought one so now I need another one to mount on my handle bar for the bar LED lights, which will probably happen soon.