I use two AAs for my camera, four AAs for my headlight, two AAAs for my rear blinkie lights, and two AAAs for my helmet light.

I can do an entire 3-month tour with the AAAs I started with in my rear blinkie and in my helmet light. If I were touring longer, I would just buy another package of AAAs.

If my tour includes a 1200K randonnee where I actively use my headlight, I might need to replace those batteries. Again, I would just buy another package of AAs. If my tour did not include much night riding, I could do a tour of several months without needing to charge or replace those batteries.

And if I get good batteries, 6 of them will last me a month in my camera ... so I just keep buying them as I go along.