I get the following for an N810 with OS2008:

Idle, offline mode - 270 hours
Idle, WiFi on, power saving mode - 100 hours
GPS chip on - 11 hours
Idle, WiFi on, power saving mode OFF - 7 hours
Idle, display backlight on - 9 hours
100% CPU (loop doing sqrt), display backlight off - 6 hours

These figures are based on extrapolating from
a graph of "battery-status" output, rather than actually letting the
battery run completely down.

The default WiFi config (under advanced/other) uses a power saving mode. This uses less power than the GPS.
The GPS driver turns the chip off if nothing is accessing it; I used a program that polls it regularly to keep it running, which will run up the CPU, too. It should be possible to save power by reducing the poll interval to the minimum, or by only turning the GPS on every couple of minutes.

http://andrew.daviel.org/N810-FAQ.html#battlast

Re. camping, Nokia make a 12 charger which should charge the battery in 2hrs from a car/boat/motorcycle/snowmobile. I didn't measure, but it should draw about 0.6A as the charger gives 0.89A
at 6V, same as the 110V one.
For wilderness camping, I'd think it ought to be possible to charge from a solar panel or hand crank. But I don't know enough about Li-ion cells to know if charging at, say, 200mA for 10 hours would be acceptable.