damm battery keeps dying

so here's the issue...i didn't drive my 1999 c2 for about 4 weeks, didn't even start it. i just had the 30k mile service done too so i assume major problems would have been brought up to my attention and hopefully fixed. but anyways, i went to start the car sat. it didn't turnover. i jumped it and then drove it about 15 miles that day, even letting it sit in a garage for about 3 hrs while i watched a movie. it started back up fine that day. so now it is wed, i tried starting it just now and it won't turnover. the battery gauge reads fine. anybody have any suggestions/thoughts/experiences? my dad's c2 can sit without being started for weeks on end. thanks!

If you're leaving your car sit for that long, why not invest in a battery tender? Once your battery has been drained, they ususally are on their last leg.

Four weeks at a time might drain any car's battery. Ask Oak suggested, you need one of these unless you can drive your car at least once a week.

what's a battery tender? thanks. so i guess letting the battery drain (ie sit that long) is NOT a good thing.

This:

oak, viken thanks for your replies. those were the answers i was looking for. last ignorant question is what exactly does the battery tender do? i know preserve the battery somehow, but what is the science behind that? thanks!

ok i lied...one more question...you guys think then i should buy a new battery?

By now a good deep charge is due, tho if the battery is the origiinal 99 a new one won't hurt then Drive the car more often or use a battery tender

Just a little info -- I have used a small tender that sears sells -- $29.00 it mounts in the car on a clip and connects directly to the battery-- comes with a short 110v cord. It is not a simple trickle charger rather it is an electronic unit that will turn completely off when the battery is charged. Have installed quite a few and they are great

A battery tender or trickle charger will not charge a dead battery - it is meant to keep a good and fully charged battery charged. If you have a 4 year old battery and have problems with it then it is time to replace it. It will never 'cure' itself. Take it out and bring it to a parts place where the can put a load on it. The battery is a standard group size 48 and you can get them from Interstate or Sears or other places. Replaced mine 2 years ago with one from Autozone for $60. Jeff

Once a conventional lead-acid car battery goes completely dead, it's on borrowed time. The lack of charge allows an adverse chemical reaction to take place. The battery is then said to be "sulfated". Once this happens, a vicious cycle ensues which guarantees the battery will be totally useless -- sooner, rather than later. I know, it's happened to me a DOZEN times in my thirty years of Porsche ownership experiences. As was stated above, the best solution is to use one of those Porsche marketed "wall wart" power supplies with the lighter adapter on a long, long cord. The small current it supplies can make up for the constant drain of modern vehicle electronics without over-charging the battery. They're worth every penny I paid for them. I HATE buying new batteries for seldom driven cars. Of course if one were to retrofit a "deep cycle" battery, at least it wouldn't be used up after the complete discharge. One could recharge it. But then, one still has to wait for the charger to work its magic. I'd still be p....d off, waiting to get the seldom used car going (nice afternoons don't last forever). The best bet is the simplest: Get Porsche's Battery Maintainer ! And USE IT!