@mustelidae,

I have been using Etrex for years.

They run on 2 2450 NI-MH Batteries.

Never have recharged the Batteries on the unit.

I keep a portable charging unit with me and 2 extra 2450 NI-MH Batteries as a backup.

These Etrex units are good for 12 to 25 hours using NI-MH batteries.

Have never run out of power doing a long hikes that last 2 to 3 days with a group of hikers.

Why do you need to be on electric power to use the Etrex??

If I need to update and GPX tracks I just plus the Etrex into my Laptop and update that goes for the maps too.