I am adding a spare, external cell phone batterey
Yes - and my energizer glowstick with a handful of batteries can go 100+ hours...
Came across these whilst trawling the internet
http://uyled.com/uyled-products/camping-lamp/Waterproof LED light and USB battery pack. Available at places like Aliexpress, the smaller 1x18650 Q7M is $14 atm.