This is the same sort of thing I was trying to do a couple years back for my solar-powered observatory.
I have a voltage monitoring device (West Mountain Radio PWR Guard Plus) that if the juice goes below 11.5V I typically want to start a shutdown.
http://www.westmountainradio.com/pro...s_id=pwr_guard
I would love to have a more complete solution for this than my hack.
Differentiating between power and WX would be very beneficial.