GPS66i power off automatically

I just received a new 66i and took it out on the trail yesterday. I activated it, loaded some waypoints with explorer app and synced up everything. I have not adjusted any of the settings in the 'setup' app. After turning it on I heard the first few waypoint proximity alarms going off so I know it was on for at least the first hour. When I next looked at it, it was powered off. I had to press the power on button and wait for it to boot-up. The exact same thing happened after another few hours, I again know it was on for at least an hour due to the proximity alarms going off. 

I've read the other threads on the auto-powering off issue but none of them appear to relate to my issue. Is there any configuration/setting that could be causing this? I purchased this unit for SOS primarily and need something extremely reliable and so far feel very disappointed in its reliability.

Thank you.