Confused with the battery for my Mini Cooper S Convertible.
 

Hi
I'm very confused as which car battery to buy for my Mini Cooper S Convertible. I called the Mini Dealership, and it recommended a battery with 450CCA, 55AMP at $150.
I looked into Autozone and it recommended a battery with 750 CCA, and cost about $210.
Walmart had a battery that was $100.
Which is the best car battery that I should buy? I live in Chicago where it is cold and I'm not sure what would happen if I buy a higher CCA battery than what the dealership has? But I hear a higher ampp is good for cold weather places? So very confused. Please provide advice, and also what brand battery is good, or what other details should I look for?
Thanks.

450 amp will be fine. A high amp battery will last longer before it needs too be jumped if you let the car sit but will work the alternator harder to charge it all the way back up. If you will only keep the car a short time buy the cheapest battery you can and stick the next guy with the problem. Best would be to buy a good quality battery close to the original factory rating of 450 amps and get a battery maintainer if you let the car sit for long periods. That will balance the load on the alternator and last for years.