Lawn mower worked great when I brought it home, but now, whenever I go to start it the battery is dead. I bought a new battery, thinking I just had a bad battery, but now, after sitting in my garage for a few days, the lawn mower won't start with the new battery in it. It started when I brought it home, and I know it had been sitting for a while at the store. Any clues? Can leaving the keys in the ignition have anything to do with this?