I second the charging system check recommended above...the rectifier connections in the tail seem to fry the connections some times and can lead to your symptoms...check the manual for diagnostics and the rear pod wiring at the rectifier...
Good luck,
I'd also investigate and check out the charging system especially since you've indicated batteries don't last. Start motors don't kill batteries however, insufficient charging does.
If you have a stock engine, the OEM battery provides more than adequate CCA to start a stock engine provided it's actually charging properly.