2003 Mazda Protege 5 door- In 2 years, gone through 3 batteries. My mom's car driven 2-3 times a week. Dealer says it's a "marginal battery". They've checked ground wires and alternator. I just feel it's the alternator or wiring issue. Very intermittent problem, but frustrating. Paying for them to have internal check - Any suggestions, comments?