Battery worries

[442nd986s]

Here's my 2 cents worth......
In a typical car, a battery can only affect HP (horsepower) if it's less than 12 volts. And by this I mean ignition and a continuos spark.
For example....
If a battery doesn't have enough CA (cranking amps) or has a bad cell, then the ignition coil or coils of a Boxster will not receive the necessary voltage needed to put out onto the spark plugs. This would equate to less premium of a spark. Less spark, less HP and/or a code.
As the old saying goes, "you get out what you put in". Think of a coil as a transformer. The coil is looking for a 12-13.8volt source to produce 30k-50k volt spark. (I'm not sure what the Boxster actually needs but it would be in that range).
I did a little research for you and have found that a MAJOR leading battery manufactuer produces your battery with the following specs:
Product ID: MTP-91
Amps: 875
Cranking Amps: 875
Cold Cranking Amps: 700
Voltage: 12

When you compare your battery to this one, as far as cranking amps (CA), your battery is good. However, nothing is perfect in life, so I would take it to an Auto Part store and have them check it out for free. Just make sure they check your battery WITH IT BEING HOOKED UP (this will check your alternater for charging output) and WITH IT NOT BEING HOOKED UP (this will check the battery independently).
After all this is said and done and everything check out fine, then you might have a bigger issue (voltage regulator, cloged fuel filter, only get 1 jiga watts of power instead of 1.2)

Hope this info helps, keep us posted.