Didn't you purchase your Boxster from a dealer? If so, you may want to contact them and see if they will replace the battery with a new OEM one. After all, you've only had the car 5 weeks.
Also, there are procedures to be followed after installing a new battery:
Replaced battery for my 2005 Porsche Boxster - 987-1 Series (Boxster, Boxster S) - RennTech.org Forums
Just sayin'............
TO