I actually tested my 500 and 810. The 810 can run when attached to power, the 500 does not. The cable that ships with Garmin units is a standard micro USB. The issue is strictly with the pinouts on the 500.
And here's the experience of a guy who did RAW/RAAM, and saw the same issues with just the 500: https://forums.garmin.com/showthread...harger&p=95222
Fortunately, it is now fairly easy to work around it, if you're willing to buy the modified cable from Gomadic. So, you do have the option of using a battery pack if you like.
OSM Map On Garmin/Download - OpenStreetMap Wiki
For the US I think I used osmmaps.com
or maybe it was VeloMap.org -Roadbike ? Bicycle ? Maps based on Openstreetmap « Windows/Linux ? VeloMap Map Downloads
For Europe I use openmtbmap.org
It's a little complicated, but not all that bad. The maps can be so huge as to slow down processing. I select an area that gives me a map size of under 4GB.
A comprehensive worldwide source is Free worldwide Garmin maps from OpenStreetMap
Don't know how other units work but I plug mine into the computer and just copy the downloaded .img files into the maps folder on the unit.
Garmin has a 50-viapoint limit on routes. But that's almost never a binding constraint if you make routes that go from control to control. Out of hundreds of rides that I have made a GPS file for, there are only a couple where there are so many turns between controls that I run out of viapoints.
But it doesn't, and neither does BaseCamp. At least with the OSM maps that I use. So I'd be curious to hear from other eTrex 20/30-BaseCamp users about this. There are long MUP's (Multi-Use-Paths) I ride, and the only way to make it route on them is to put viapoints between every intersection. Then there is the limit on viapoints which presents a different set of problems.
I even tried creating a walking route connecting two ends of a MUP. BaseCamp used the sections of trail at each end but routed most of it on River Road and some of it even on the interstate. I'm going to put in the suggestion as mentioned above, but in the meantime working with tracks instead of routes seems to be the best solution for the newer eTrex units.
It's funny how everyone today is hooked on technology for navigation. Get a map and chart out your route. It's much more fun!
I think the fact that so many of us are hooked on GPS technology is a good indication that we have more fun riding with GPS than with a printed map. I have done both and far prefer the GPS. It's good to hear that some people stick with the traditional ways. (Different strokes for different folks. Variety is the spice of life. And all those sorts of aphorisms...) You may have more fun with printed maps, but I'm sticking with my Garmin...or in a pinch, even my iPhone.