Hi moonpie,just measure the battery-tray and order the largest battery that fits. Your alternator charges any "normal" battery nicely
and you'll have good power to start plus keep those beers in the cooler nice and cold too.
Remember-even if the new battery comes "dry-charged" Don't just install. Take your 4 for a good spin (at least 1hr's drive)to properly
top-up your new battery Or couple up your charger for a couple days.It won't "over-charge" so no worries.... -Reid.