Look at the ratings, you want the highest CA (cranking amps @ 32�°F) and CCA (cold cranking amps @ 0�°F).
Then just look for the best warranty, also I suppose brand names would be best (maybe Die Hard from Sears, see stuff on TV about them a lot...)
That's about all I know, the more CCA, the better it will start the car in freezing weather. My old Cadillac had a gargantuan battery with over 1000 CCA (like 1500 CA), thing started one day in -10�°F temps when my mom's 6000 with a new battery wouldn't.
