Battery problem...

[oranje]

Hi there - didn't use my Boxster (2005 987) for a few weeks and then had trouble starting it, it only just cranked. So I thought, let's drive it for a while and recharge the battery.

Next day, same problem - could hardly start it. So I took the battery out and tried to recharge it. Unloaded voltage was only around 10.8. Charging seemed to go way to0 quickly, an hour or so. After charging it showed 12.9V unloaded, but dropped back to 10.8 over night.

I checked the fluid levels, and they're all above the min, and below the max. However, shining light through the cells and knocking the side of the battery, I saw gas bubble up in all but one of the cells. Suspicious I thought... dividing 12.9V by the 6 cells is 2.15V per cell, times 5 bubbly cells is exactly the 10.8V it dropped down to...

So I decided to unscrew the vents and have a look (wearing safety glasses, of course!). Again, the bubbly cells all looked the same inside. The quiet cell looked different. A picture is attached. The one on the left is a bubbly cell, with the plates covered in dark stuff, the odd one out has the plates clean.

It appears I have a bad cell. Is this fixable? Is this my fault for not driving for only a few weeks? (seems quick for it to go bad) Is this a warranty issue?

Many thanks!

Jan