I'm a big believer on everyone having dashcams in their cars, (I'm not even sure why cars don't come factory installed with them, but thats besides the point of this post).
On all my vehicles i've always installed them in the front and rear. The Volt has a fuse box in the rear that makes it easy to tap 12v power from but all of those are always on (not ACC switched). I installed a mobius dash cam in the rear over 2 years ago and although it draws very little power, if the car is left parked for over a week the 12v battery can drop to near 11.2V (almost dead).
My solution was a to wire in a low voltage disconnect module. I have it set the cutoff at 12.1v and reconnect at 12.6v. So far so good, stays on after I turn ofF the car for 20+ minutes. If anyone is thinking of wiring a rear dashcam to the rear fuse box, the module can be purchased from amazon.
The voltage cutoff and reconnect is easy to set with dip switches.