I forgot to mention I have upgraded all my electronics from: head lamp to radio, to all be powered by AA batteries.
Why? Because AA batteries are cheap and easy to find. Currently I use rechargeable 2400 mah AA NiMH batteries.
What I do is load up the lights, radio, etc. with batteries fresh off of the charger and put spares in a pelican dry box. That way I do not have to worry about sparing battery use.
On emergency charging, here is a handy product that I have not purchased yet but will soon. It fits with my philosophy of cross compatibility: