It took me a while but I have figured out my problem. My Acer R7 would charge sometimes and then stop charging. I would wiggle the DC plug and it sometimes would start charging. If I didn't notice the discharging condition the computer would just go black.
Turns out the culprit was the DC jack where you connect the DC plug needs to be grounded by way of firmly touching the case. When new it was attached to the case with what apparently was conductive tape that long ago went bad.
The fix is take the twelve screws out of the back case cover and lift the DC jack out - it's not fastened other than the tape. Lightly roll up a 1/2" square of tin foil and put one under the jack and put the jack back in and then put the other on top of the jack. Carefully put the case back on without disturbing the foil and screw it down.
