discounting that you've probably hurt your battery bank by running it that flat, we need to establish if there's any current flowing into them from the panels at all. it's entirely within reason that batteries on a low charge from completely flat would show that low a voltage. shut off your loads and watch the battery voltage. if is doesn't recover in a few hours, you're in for an expensive time.
if you happened to check on the PANEL side of the controller and got 9.xx volts, but 20V measured directly at the panels, I would suspect that something came uncrimped, unsoldered or otherwise partially unfastened somewhere in the transmission wiring between the panels and the controller. disconnect the batteries and check again. . . if the voltage comes up, (on the PANEL side of the controller again) I'd suspect the supply side wire.
no change? disconnect the controller and try again. if the voltage comes up, the controller is suspect. if not, you probably have a damaged panel. . . . even with really BAD connections, if the panels are putting out, you should see no significant voltage drop with no current flowing.
these are checks you can do from the battery room without going into the cold or disabling the car.
if you got 9.xx Volts on the battery side of the controller, and the 20V reading was on the panel side of the controller, I would agree with Ghurd; but let the car battery equalise with room temperature for a couple hours before putting it on charge, if you can. (the open circuit voltage of L-A batteries changes with cell temp.)
then, once the car battery is connected, monitor the battery voltage a couple times an hour for a full charge-day. if there is no rise, (or worse, a drop!) then follow the steps in the first two paragraphs to isolate the problem.
remember to shut off all your loads during these tests.
-Dan
