Consider parasitic drain

Hi, I wondered if you could give me some advice or feedback. My 08 Cayman has been getting weekly use all summer up to now, and by that I mean use that would be easily sufficient to keep the battery charged. Over the last several weeks, however, I've noticed it cranking very slowly when getting ready to go out. Today it cranked very slowly but started, and we went out and ran several errands, then after stopping for a couple of minutes to run inside the store, I came back out and it wouldn't start. Fortunately I was able to roll-start it and got home okay. I guess it's just time for a new battery, but I'm concerned that it might be something more because (a) up to now the car has been run weekly and if not, the battery tender all the time, until a few weeks ago, it was just fine, and (c) I haven't had any warning lights indicating a charging problem. And another thing, my battery tender has LEDs that indicate the condition of the battery. When I got home, I turned off the engine and it restarted easily. Nevertheless, I connected to the tender, and it showed 25% charge, but within an hour it was showing 100% charge again. This seems really strange because normally it takes hours to get to 100%. The tender itself seems to work fine and I've never had any problems with it on the Cayman or any of my other cars up to now. At the moment, I'm leaving the tender connected with the idea that I should be able to at least start the car to take it to the right place to have it worked on!

Other facts:
* Bought this car new in April 09, presumably after it sat on the dealer's lot for several months ... however, it never showed any problems until just the last few weeks. Seems like a battery should last longer than just 2-1/2 years of service, considering the care I take with it.
* I added a new aftermarket amp and subwoofer last August to complement the Pioneer AVIC, which was installed over a year ago. The radio seems to operate normally in all respects; i.e., it seems to shut down normally when I turn off the ignition, but is it possible that the amp is nevertheless not actually shutting down and is quietly draining my battery? Now that I think about it, the timing of installation of the amp kind of links up with the battery problems. But how could I tell?
* I don't want to bring the car back to the dealer to have them check it if I can help it. Not only are they 40 miles away from my house, they also have repeatedly demonstrated gross incompetence and generally aren't very pleasant to deal with anyway. And at Porsche battery prices, even if there is a prorated warranty, I'd still be better off to get my battery somewhere else. I don't care to go to the hassle of taking the car 40 miles only to have them charge me an arm and a leg for "diagnostics" plus $250 for a new battery. I do have some warranty work that I'll be forced to go to them to do (replace the horn and the cupholder) but that is hardly a high priority and frankly I'd rather avoid having them touch my car except when I absolutely have to.
* Thinking of taking the car to my usual indie mechanic whom I trust and having him check the battery and the charging system, and maybe the amp, if he can do that (or would I need to go back to the amp installer to check to make sure it is shutting down?). If the charging system is okay, then I'd let him replace the battery which he can do at a reasonable price (based on past experience with my Boxster). And he could do my next scheduled maintenance at the same trip.
* Another thought in my head was just to keep the battery alive with the tender until next spring, and THEN take it to the indie and doing the same, the idea being, why get a brand new battery and then just garage it all winter long? However, I'm a little scared that it could go totally dead notwithstanding my efforts and then leave me with issues about getting back into the car to replace it.

Any help would be appreciated.

The slow cranking plus the fact that it takes only an hour to obtain 75% of charge from a battery tender indicates that your battery is toast.
Although batteries often last longer than 6 years, they sometimes die within 3 years.
To be sure you could have its capacity tested at a battery store.

Hope this helps,
regards,
Joris

it may just be a bad battery, one that developed a premature problem. That's what the warranty is for, although IIRC batteries may not be covered for the full new car warranty period, but say only 12 months from date of purchase.

Some new car batteries suffer premature failure not because the battery is, bad defective, but simply because the batteries lose too much charge while the car sits on the lot. I have driven by dealers where a tech is out and starting up the cars to let the engines idle and recharge batteries (not sure how much recharging this accomplishes) and in the times I've seen this maybe one fourth of the car had their hoods open and at least one had a jumper battery connected. The cars with the open hoods suggests their batteries had run down too much to start the engine without help.

Anyhow, my local dealer uses an Interstate battery but the model it uses is made in Spain (label on top of the battery case states this) and the techs tell me the battery is of a very high quality.

Be sure you get an exact drop in replacement battery. And be sure you check with the dealer's part department to see if Porsche upgraded the battery called out for your car. Porsche did this for my Boxster, the stock battery had been superceded by a larger -- longer -- battery with more AH's and CCA's. While the battery was physically larger, longer, it was the same height and width and dropped right in and the hold down hole in the bottom of the battery box had a threaded nut so the battery hold down screwed in and held the battery secure.

You need to check that the electronics/music hardware is not drawing the power down while the car sits. The security system is partially disabled after 5 days to save battery power but the existing car electronics can't know and do anything about an aftermarket electronics/electrical device that is a new and another power drain.

Sincerely,

MarcW.

Unusual power drain when "everything turned off" - easy enough to check with two people and a multi-meter set to current draw, I know you have a 987 but the 986 current draw against time chart is on my site under the batteries section.

Amp - see what happens if you just disconnect the amp for the woofer. I suspect that something to do with the install is the root cause though it may have also bled over into taking down the battery too.

Battery - load test and if it turns out to be just a tired battery, then be assured the Porsche battery is nothing special. I used an Optima just for fun even though it cost $50 more than others just because I wanted to and it was easy to rationalize because ti was so much cheaper than the one with the expensive logo on it.

Charging circuit - load test

A good battery tester that also will measure the charging circuit costs about $100 and pays for itself the second time you use it. I'm known in my neighborhood for having one and it saves me as I borrow things from other neighbors I don't have to buy for occasional use.

buy a battery from them.
My battery was flat and I assumed I'd need a new one. I called AAA but when the local guy came he warned me that the battery they had wouldn't work satisfactorily on my '02 Boxster.Since he was already there and offered to run diagnostics on my battery I said "do it".
It turned out the battery was fine, just needed a charge (light left on, door open??).
I charged it and it's been fine for weeks. My point is the AAA guy has great diagnostic tools and if you're already a member, go for it.

I called the stereo installer and they think the amp must be installed properly because if it was not shutting down when the ignition's off and the key's out, it would be drawing enough current to discharge the battery overnight. Since that hasn't happened, they think it is indeed merely a weak battery. Therefore I scheduled the car with my usual indie mechanic on Friday, and he will run a diagnostic on current draw and install a new battery for $200 (I also called the local Porsche dealer and was quoted $340 for a new battery alone. Fat chance of that). I know I am capable of replacing the battery myself quite a bit cheaper than $200 but I don't know how to run diagnostics. The indie's test results should provide peace of mind and give me evidence to argue with the installer if there really is an issue related to the amp, and, he can do my annual service at the same time. I like the indie mechanic. Aside from my bad experiences with the dealer, this guy is fairly reasonably priced, he lets me watch him work, explains things, and talks to me like I'm not a complete idiot. That has a lot of value to me.

I had a similar problem on my 2002 Boxster S. The battery would take a charge, and voltages across the terminals while running showed the alternator was charging properly. However, after 2 to 3 days, the battery would be nearly dead. Took it to an AutoZone parts store, where they checked the battery with a load tester FOR FREE, and it tested out fine. I used an ammeter and found there was a constant drain of 2.5 amps while the car was shut off. I.E. parasitic drain. Back to the Porsche dealer, where it took them a lot of testing to find that ONE alternator diode was bad. It had dropped the resistance to ground from infinite to a few ohms, and current from the battery was flowing reverse through the diode to ground. But it charged fine, when running. Replaced the alternator and no problems for the last 5 years. Just a fluke, I guess, but worth looking at before buying a battery you might not need.

It was just a bad battery. Drain and charging system tested within normal limits.
Thanks for the help.