My 446 starts well when it is cold (cranks pretty well...but not vigorously). However, twice I've had the tractor stall because I struck a object bother with my mower and today with a snowblower. When this happens the tractor won't crank over (i hooked it up to my car and it cranked vigorously and started right up. I know the battery is old and I assume this is the issue. Any idea why it would be so hard to crank when the engine is hot?