I see most people are advocating an aviation-specific Garmin GPS.. I'd certainly not disagree that these are excellent units, I've used a number of them and was very happy with their operation.
However to answer the original question I don't think it's
necessary to use an aviation unit, particularly if you're cost-conscious, or are looking simply for some local landmark pointers/groundspeed/eta/goto functions. I've extensively used a Garmin GPS72 for just these requirements and it works fine - at a significantly lesser cost than a 196 or similar. I can load into it an aerodrome database and use the simple goto function to give me direction/eta/gs/elevation etc, all very useful stuff. Obviously you wouldn't use it in IMC
and it won't give you airspace or terrain warnings but, arguably, that's what maps are for
and you'd use such a GPS to augment your position reckoning. Additonally, as I think the good Dr has done, you can feed the NMEA data out of the GPS to a moving map display on a laptop. This works well and if you were to use a smaller laptop such as an ASUS ePC or Sony Vaio you can end up with quite a good system. Some of the later moving map software packages will display in 3D as well as a number of other functions that perhaps make them just a little more versatile than a fixed-purpose GPS. Incidentaly you won't lose the GPS functionality if you're concurrently outputting the data to a PC. I often d/load my tracks to such software so I can accurately log my flight time and also see if I could have improved my route amongst other things.
Just to mention other makes I know a few people who have used the Lowrance (Aviation) units with some success and satisfaction.
On batteries I'd get a good set of quality hi-cap NiMH cells, and a spare set, and a spare set. I use SONY 2.5 AH AA's in my Garmins, sure I can get cheaper batteries but over the years (and I'm in the know!) I've found they're not all created equal. And yes I do usually carry at least two spare sets. I also try and use equipment that has the same (AA) battery type, such as the camera, torch etc so that I may have other sources of power in an emergency. Backlighting will use up more power but a fully charged set of batteries will almost certainly outlast your fuel tank even with it switched on.
FP.