I have 2 riding mowers and both have the same symptom. Battery wears down after 1.5 to 3 tank fill ups.
Both Craftsman green, both 1999 m/y's (IIRC)
1st is a 16.5HP 42" HST mower
2nd is a 20HP 46" HST mower
I have a feeling the electrical part that keeps a charge going back to the battery is...