Low battery symptoms

[Steelepuls]

Originally Posted by KevinH1990

My Boxster failed to start once last winter and I had to jump start it. During the last few weeks if I drove a short distance the car sounded like it was barely turning over when I restarted it. I checked my records and the battery was 7-years old.

I decided that I was risking another failure and replaced it with an Interstate AGM battery in size H7 (94R.) The H7 is larger than the battery I removed (Bosch 48-690B.) The H7/94R Interstate battery is rated at 850 CCA. Consumer Reports tested a smaller H6 Interstate AGM battery which the manufacturer rated at 760 CCA. It rated the life expectancy as 5/5, the CCA as 4/5 and the reserve capacity as 4/5. They rated an Optima H6 ($290) and an Odyssey Performance ($260) slightly higher than the Interstate.

The AGM batteries are more expensive. I paid $175 at Costco. However, the information I've been able to find indicates that they are better able to tolerate a situation in which the car is not driven for an extended period. Although I normally drive my Boxster several times per week, we had some ice and snow during the winter and I didn't drive it for about 10 days. That is when I had the starting issue. The AGM battery also has a 3-year full replacement warranty.

Kevin, I had the same issue with my 01S, where the first start is cold it has no problems turning over, but after a short stop to get gas or pickup food, the restart is slow. When I leave it for over an hour or two inbetween stops, the problem is not as noticeable. It isn't a battery issue or alternator, since those two were replaced recently with new parts. I've read here that the alternator wiring harness is heat soaked and causes the slow turnover.
I haven't confirmed that since i haven't fixed this yet in my car since it has always started, albeit slow. The harness is not too expensive, but I've heard it is a bear to replace.