I have a one year old Exmark 27 hp Kohler. It has the factory no maintenance battery still in it. A friend just gave me a new "Wal-Mart" battery with 325 cold crank amps the same as the factory battery. The new battery is a conventional maintenance battery. Should I take the factory battery out and put it on the shelf for back up? OR Should I leave the factory battery in and leave the new conventional battery on the shelf for back up? How long will the new battery keep on "The shelf?" I appreciate anyones insight.