For a good basic unit, the 76 series are nice. Not very high tech but they get the job done. They use standard AA batteries and will run about six to eight hours on a normal set of disposables. They are very durable as well. I used a 76s for a couple years on my bike and for geocaching. It got dropped in mud, pelted with rain, and held up to the vibration of being mounted to handlebars of the Wee for countless hours, and still works like a charm.
is exactly what you're looking for. It uses either it's own rechargable (CRV-3) or two AAs. The setup I have includes a RAM mount and a Powerlet connector for on-bike power. It's waterproof, hand portable and uses SD cards in addition to its own built in memory for maps.
I love my 76CSx. Batteries last a long time, and the best part is it uses AA, so if I ever get stuck without batteries I can hop over to the nearest store and buy a pair. The only drawback to not being hard wired is that the backlight only turns on when giving directions at night. I mostly use it during the day, so that's not really an issue.
FWIW, I got the Garmin handlebar mount with the GPS and it's been good since I got it.
I agree with shawmutt, the 76 CSx is great, no need for hardwiring it in and the batteries last well enough. I have the Garmin handlebar mount as well as a custom made mount. (I wanted the GPS in a better line of site than where the Garmin mount places it.)
For what it's worth, the Garmin 60Cx, 60CSx, 76Cx and 76 CSx are essentially the same GPS. The 76 versions are physically slightly larger and float, the "S" versions include a magnetic Compass and barometric altimeter. I suspect that, unless you are using it for hiking there is little if any need for the Compass and Altimeter. (I use my 60Cx in my airplane, car, and on the bike and a few times for Geocaching and it works fabulously.)
For all of them you will need to purchase an additonal Map Program and likely a Micro SD card if you want to have detailed street maps and the ability to have the unit calculate routes for you. (City Navigator v8 for all of North America fits on one 2 gig card. I don't know about the latest version.)
My garmin 60Cx has been great, but if I was buying a GPS for the Bike today, I would buy a Zumo, but it wouldn't satisfy the battery issue for you.
So, what is your range?
How far do you normally travel?
My range became too great for my Garmin GPS V, so I upgraded slightly to the Quest.
I'd make you a hell of a deal on the GPS V with mount, car mounts, hard wire, if desired...