My car recently has died twice and I don't know if it's the battery or the altinator because both are new. The battery is 3 months old and the altinator is 5 months old. I had my car jumped and it ran fine then I got it home and didn't use it for about 5 days and the same problem happened again so it sat for about 2 weeks before I got it jumped again and it started up with no problem. What could be causing this. My car is an 1988 bonneville with 174,000 miles. Is it because it's been sitting awhile?