Posting this in case others may be have the same issue as this, but perhaps think it's an internal on PCB contact problem (which I did). Fortunately because I still had my old Etrex Vista HcX with the 4hr battery life, I've been able to scavenge the 'base' battery contact to replace the cracked one in my newer ebay Hcx unit.
I first noticed there was a problem when the unit would turn off when 'snapped' out of the handlebar holder, or if one knocked the unit on the top. (It hadn't yet turned off while on bike during a ride) With the back plate off I found that I could turn the unit off by pulling back on the cracked contact with my fingernail... owing to the reduced 'spring'.
