My battery light came on along with the two little green lights, flashing. This was after a long trip from Portland to Seattle and back. So I cleaned my battery posts and cables. Problem solved. So far. And this occurred two weeks ago. But I will be diligent about watching the alternator.

 

If you do end up getting a replacement battery pay close attention to the CCA (Cold Cranking Amp) rating. Yours at 690 seems a bit low for the weather you're dealing with. I have seen Group 34 batteries with 800CCA rating which would probably serve you well in the cold temps you are dealing with. Check your oil viscosity, too. Definitely want to run a 5W-30 or 5W-40 in those crazy low temps to make starting in the morning easier. Maybe even consider one of those Mobil-1 full synthetic oils with 0W-30 or 0W-40 rating?

 

I did get a new battery. Got the wrong one!

But just finished putting in the new used alternator and everything looks good!

 

Get at LESS a 800 cca battery