I just inherited my Dad's 2000 Buick Le Sabre. Always garage kept. I park outside. Temps have dropped below 40 twice this month and both times car won't even turn over. Lights, bells etc still function. Wait a couple of hours and car starts right up, no problem. Had battery checked, starter o.k. Mechanic says it's a Florida car and doesn't like cold weather!! Battery under back seat. Any ideas? Thank you.