The little clip supplied with the Etrex color units slides into the Garmin mounts.
I've used Garmin mounts before - They aren't designed to be hit by anything.
I currently use Ram-mounts on my mountain bike - lifetime warranty -
cradles for almost anything so I can use different units easily.

Regarding the eTrex shutting off with 2/3 life left - You probably did not tell the GPS what type of battery you are using it with.

I prefer a larger screen as on the 60, 76 or Colorado units.
Have a Colorado 400t on order from Garmin with a heart rate monitor.