The car may sit for 5-7 days at a time. I don't want to spend over $300.

 

braille 21 lb served me well. as long as I drove the car once a week it never had an issue. if it sat closer to 2 weeks it would still start but you could tell it was weaker.

 

braille 11.5

 

Or is that model #

 

The Odyssey PC925 served me well in my S4. Never had any starting issues even when it sat for a few weeks. It was great even during winter (in the negatives) startups. But it's a bit bigger and therefore heavier than the braille's or the PC680.

 

Deka 21 lb = Braille without the sticker at half the price...

 

If it's one wek, any good battery should do. Even my OEM battery handles a couple of weeks without a trickle charger no problem (not that it ever really goes a couple of weeks very often). I think the need for a trickle charger is more due to the car than the battery. These cars continue to draw power (seems like a little more than most) just sitting there. With any battery, you'll likely need a maintainer if it's going to sit for long.

 

I'm not sure how well this would work on a Porsche 996 ('ve killed the battery once and it was a bit of a PITA to get things back in order), but when I used to run an 11.5 pound Braille batteries on other cars I'd just disconnect the negative terminal and than re-connect it when I was ready to drive the car. I never had a single problem with the battery when I did that.

Since the 996TT 'trunk' is battery operated, you'd need to plan ahead and leave it open resting on the latch, but this may be a viable option if others can confirm it. For the record I don't mess around with lightweight batteries yet on my own 996TT and the one time I killed the full-size battery it was my own fault. I got to spend some quality time with the owner's manual after that!

 

+1 for PC925