Replace or Recharge Battery

If you're going to keep the battery or want to know in the future how good the battery really is check it Old School...If the cells are accessible (and many still are even though the unit looks sealed) check each one with a simple acid test squeeze bulb you can get at any parts store. If the electrolyte has been allowed to go below the plate and you had it on a maintainer, forget it. Fill the cells with distilled water and charge away, then you can check each cell. My battery is at least three years old and it's fine but I'm careful to never let the acid level drop or charge it partially dry.

[Norminhouston]

The Moll battery on my '03 BoxsterS lasted approximately 6 years. I think that is pretty darn good. As mentioned, it is important to check the fluid level regularly and top off with distilled water. The original equipment battery is certainly overpriced. I went with one purchased from AutoZone when the orig bellied up.

[Lil bastard]

@mikefocke... I agree with your testing but your values are a bit off. A healthy battery will produce about 2.2VDC from each of the six cells which are wired in series, so the battery total should produce closer to 13.2VDC. If the battery is less than that, it is either not fully charged, low on electrolyte or has broken or sulphated plates, all of which can happen to a battery over time. So, a range of 11.9 - 13.2 is probably in order.

The same goes for the alternator, a range instead of an absolute value. Bosche rates the alternator with an output of 13.5VDC-14.5VDC. Anything in that range is OK.