I put a 9ah motorcycle battery in the trunk at the back of the bike for fun.... 9 hours later it had used 2000mah. I'd bet you could run that for days without charging on a tour. Sadly the battery weights almost 3kg and its more weight than I'm willing to carry. Just got some Energizer 2450mah batteries. Going to see how long they last. At best estimate from the 1600mah lipo that died at 6 hours I would say 6-8 hours before the voltage dips too low to run the usb adapter.