said by Cho Baka:If it has been down for 9 days in sub zero temps, you likely have bigger problems.
A fully discharged battery can freeze.
Do not charge a frozen battery, it is dangerous. Both fully discharging and freezing a battery are bad for them.
Seconded.
I'm Floridian, and haven't seen snow accumulate on the ground in all my life, but it seems to me that your panels are steep enough that snow wouldn't accumulate on them. Long term overcast could have run it out of power, but the solar should have recovered it when the sun came back, unless something is broken. I think you'll find the batteries frozen and split open, or something else in need of repair. Examine the batteries closely before attempting to charge. Good luck, it looks like a well setup station.