How about wiring 6 x 2V cyclon J-cells(5 AH) to give 12V or 7 to give 14 volts and using a hair drier to shrink a clear plastic drink bottle around them. Then zip tie them into a water bottle cage. Cyclon (nee Gates) cells are tolerant of deep discharging and recharge quickly. Very rugged as well. My original Night-Sun used a pair of 6 volt D-cell battery packs. Yes sure NiCads and NiMH are nice but pricey for me. I'd save lithium for Paris-Brest or RAAM.