Originally Posted by Chaditotx

Sounds like a battery. Limited usage can be a killer for batteries, though I am not sure this is your case. What brought that to mind are reported mileages for a cat like the SC430. As an ex service manager I saw tons of battery failures. When I was at Peterbilt, I saw few. That's because those trucks constantly ran and charged.... Most all had at least 4 batteries too due to the size of the motors. You wpuld think 4x failures but not so. The most batteries I saw fail was at Harley Davidson. It was so bad the factory was constantly hounding dealerships on the warranry situation for batteries. People would buy the bikes, and not ride them for 6 months, and turn around and try to warranty the batteries when they wouldn't hold a charge. The answer was trickle chargers, and we started installing them as a matter of course on new motorcycles.
Be wary of voltage readings when testing either batteries or alternators while they are in the car. I have seen both have acceptable voltage, but not have sufficient amperage to do the job.