Years ago, I bought a Garmin GPS II+. Monochrome display, no mapping but it would run a long time on a set of batteries. Carried it all over the place. It finally died this spring after 10 years. Excellent unit, kinda miss the simplicity.
I bought a Garmin Oregon 450 and added the topo maps to it. Love it. It won't run as long on a set of batteries as the old GPS II+ but then it only eats two AA cells at a time, not four. I used it extensively to track our hiking and canoeing with Boy Scouts last week. Had one already-used set of AAs in it, replaced those after the second day. Made it up to the next-to-last day of the trip on the second set. I'd estimate that Garmin's stated 16-hour battery life (running) is about right because I was using it 6-8 hours/day continuously recording tracks. I'm still getting used to all of the Oregon's features but I'm sold so far.
I've also used some of the simpler/cheaper current Garmin handhelds, like the eTrex series. If you want a simpler non-mapping unit, these will work just fine and are a third the price of the Oregon 450.
I also have a Garmin iQue3600 combination Palm PDA and GPS. It's purely a car or desk toy. Battery life is zippo, less than an hour running the GPS (5-year-old Li-ion batteries that are a PITA to replacs) but it's a good navigational aid in the car. It is also discontinued and no longer supported with map updates, so it may be time to buy a Nuvi for the car when the iQue finally dies.
I'll stick with Garmin and buy the model that fits the application I have in mind.