I think I didn't point this out here, but a guy on Spyderchat discovered this battery going on Amazon for what is I believe an unprecendented price for lithium ion:
https://www.batterystuff.com/batteries/ss51913.html
It is approximately 10Ah for 150 bucks, which is a great deal. A bit more powerful and higher capacity all things considered than a typical 30lb battery found in a Corolla or Civic or something, and only barely cheaper.
That alone should be quite adequate for most climates, but if you're in freezing temps some supercaps might help the car start since lithium ion doesn't do very well at low temps.
My car battery is probably on its way out so I am going to buy one of these soon.