Hi bjones. I have an '04 550. When I bought it 3 years ago, it had a lawn and garden battery in it and they last a lot longer than the small atv/utv batteries. I'm not sure the battery has any effect on the firing of the cylinder since it fires off the flywheel magnet and the coil. But ya never know. I don't know if you looked at my thread or not about the overnight compression loss, but as Travis said, sometimes they have a mind of their own...
Roger