I may be in the minority here, but if you turn your phone (& electronic gadgets) off, the rate of discharge approaches zero and a simple LED flashlight (or headlamp) with AAA or AA battery(ies) lasts a really long time, so this sounds like an unnecessary first world problem.
If you're going camping, try going minimalistic, it's really very nice - enjoy the solitude, peace, and quiet. Or is the sound of silence too deafening for ya?
Just my opinion, and if you don't share it, that's OK, keep the discourse civil.
