My step son's Mule gets hard to start when he's been using it some but he doesn't use it for very long.  The battery gets so it still spins it over but it gets hard to start.  I've noticed that when the battery is fully charged that it starts and runs easily so I'm wondering if the battery gets low, then maybe there isn't enough voltage to both spin the motor and also get a strong spark and run the fuel pump at the same time?   If that could be possible I'm thinking that maybe a larger battery, more like what's in a car might help and then keep it on a trickle charger when not in use.  Any thoughts on that?