I've found that many of the new "charged" batteries at the big box stores, still need a charge.
If you are planning on keeping your car then spend the money to buy a good battery from your local auto shop. Chances are they'll install it for free, make sure it's fully charged and stand behind it.
Then I'd buy a good battery maintainer (not just a trickle charger) for about $30, and keep it plugged into the battery when you're not using the car.....typically they help extend the life of your battery.
At least you know what's wrong and in the "big picture" of Porsche ownership got off "easy".
__________________
98' Boxster
|