Dead battery after two weeks...normal? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Ricochetron · 02-07-2010, 04:31 PM

I recently purchased a 2007 boxster. It had a dead battery when purchased so the dealer gave me a new interstate battery. I fully charged it, installed it and the car was not driven for two weeks. I go out to get in the car and find out the battery is dead, reading 4.1 volts on the battery terminals. Are these cars battery hogs?

I have decided to get away from wet acid batteries and order an Optima for the car. To avoid ruining the new battery would you recommend that I install a battery cut-off switch or trickle it after every drive, which will be once a week or so.

I have never owned anything which pulls the battery down this quick!

Boxtaboy · 02-07-2010, 06:01 PM

That's not normal. I've gone three or four weeks without driving my car, and it still started right up.

ChrisZang · 02-07-2010, 06:33 PM

let's start with the obvious: You could have a dead battery, go to a good car parts store, they can check if the battery still holds a charge

If you pass this test, then my next question is if you recently added any new "stuff" (Amp, Navi, etc)

And last not least, buy an amp meter, disconnect the + cable from the battery (but only if you know your radio code) and measure how many amps are flowing when the ignition is off, by inserting the amp meter between the + pole of the battery and the cable you just pulled off.

A little theory: if you have a 50 amps / hour battery, that means that your battery can supply 50 amps for one hour - or one amp for 50 hours. So in your case if the car was standing for 14 days = 24 * 14 = 336 hours , a current as low as maybe 0.1 ~ 0.2 amps can drain your battery. I'd guess that you need at least half of the juice left in the battery to crank the car.

So look how many amps are drawn and if you find a reading above let's say 0.1 amp, start pulling fuses from the fusebox until the amps drop.
Then you found your culprit

Lil bastard · 02-07-2010, 08:04 PM

What you describe is not normal. If the battery is new as you state, then the charging system, parasaitic draw or shorts are suspect.

Pull the battery completely and charge it using a charger with no more than 1.5Amps - Yes, they make 10 or 15 Amp battery chargers, but these are for convenience and NOT battery health. Using more than 1.5 Amps can overcharge the battery and overheat it causing water to boil out of the electrolyte ruining it's balance. The water vapor will vent from the battery and you will damage the plates reducing the battery's ability to accept and hold a charge.

Once charged, take a DMM (Digital Multi-Meter) and check the voltage across the battery terminals (not connected to the car), this should read approx. 13.2 VDC (each of the 6 cells in the battery produce approx. 2.2VDC (X6 = 13.2VDC).

Now connect the battery to the car and start it. Again check the voltage across the terminals (cables connected). It should now read 13.5-14.5VDC This is the power supplied by your alternator. If voltage does not fall in this range, suspect one or more of the 3 pairs of diodes in the alternator are bad requiring replacement of at least the diode pac (if alternator has some miles on it, suggest replacing with a rebuilt unit). Also, remove front engine cover and check deflection of te drive belt - it should be tight with no more than .5" deflection.

Finally, turn off car, disconnect the negative terminal and connect the DMM between the cable and the battery negative terminal. Your reading s/b less than 50 milliamperes. If more than 50 milliamperes, check that all doors are shut, nothing is powered by the Cig Lighter, trunk and 'Frunk' are closed and not powering their lights. If all found OK, go to the fuse box and one-by-one, remove each fuse and check DMM to see if there is any effect. Replace the last fuse before pulling the next. If the DMM drops when a particular fuse is pulled, there is a short somewhere in that circuit which needs to be found to remove the excess draw on the battery.

Cheers!

Ricochetron · 02-08-2010, 06:27 AM

That's a lot of good info to check. Once I get the optima battery I will have things checked out.

To answer preious questions, The car is completely stock with 9k miles. When I had the car delivered to the house (too much snow when bought) we had to leave the car running in the trailer to assure it started when it made it to the house (15 minute trip). We alreaedy knew the factory battery was bad and a new battery was on order. When I got the new battery, I trickle charged it to full charge then installed it. I then started the car and ran it for appx 15 minutes. The car was put back in the garage and two weeks later it was at 4 volts. There had to be a major draw somewhere or the new interstate battery was a dud.

Since the original battery was bad and the car probably required several booster starts, do you think the alternator was damaged in the process of jump starting?

70Sixter · 02-08-2010, 09:00 AM

Could be alternator/regulator if it discharges while driving.

Interstate batteries are good quality and warranted. If it is defective you should get a new one be reimbursed.

I routinely plug my Box into the battery maintainer when I park. I never know when I'll drive it next. Certainly if not run for a even a week it should be on maintainer.

Batteries hate recharges from low state of charge and will last longer if kept charged.

Ricochetron · 03-07-2010, 03:21 PM

Ok, I just installed a new Optima 34R battery with adapter plate. Battery is full of charge. Before connecting the negative cable, I checked the parasitic amp draw and found a whopping 1.2 amps. The 07 987 is completely bone stock. I unplugged the front boot light to get an accurate reading, (doors closed, everything in the off position.)

Is this what I should expect? No wonder why my earlier new Interstate battery went down to 4 volts in two weeks, ruining the thing.

vath2001 · 03-07-2010, 05:43 PM

Step 2: With the amp meter hooked up, start pulling fuses. Pull a fuse, check the meter and re-install the fuse if no change to the meter. That will narrow down the circuit.

jcb986 · 03-08-2010, 05:50 PM

Disconnect the front and rear trunk lights and then check your amps. Guys have had the switch go bad and these little lights will run down your battery if left on.

stephen wilson · 03-09-2010, 06:47 AM

Did your air bag light come on after the battery died? I left the lights of my 06 on, now I have a fault showing. I presume I'll have to have the dealer reset it?
Thanks,
Steve

SStiebers · 03-09-2010, 01:31 PM

I agree about the fault. Mine went dead when someone set off the alarm and it died, i had a lot of faults and resets, you might want to make sure everything that has to has been reset. also the light switch, i did have a bad one. Other than that i store mine from october to REAL SOON i hope, and i only start it every couple of weeks and it is fine. These cars do not draw much if anything.

ed95682 · 05-25-2010, 12:29 PM

From the many previous Post I've read, it seems "normal" for the batteries to go dead after a short rest of 10+ days. Not that I'm liking this...as I've had my '06 Boxster S for 18 months and already I've replaced the batteries three (3) times! I have not been able to figure out where the electrical draw is coming from, as everything seems to be "off" when it sits for 10+ days.

A question I have would be: If you've locked the doors on the car and the battery becomes dead, then what do you do?

I know what to do if the doors are unlocked and accessing the fuse box, but if the doors are locked, how do you get access to the trunk to jump start the car? This situation hasn't happened, but I'm imagining that it can.

stephen wilson · 05-25-2010, 02:41 PM

You might want to talk to the dealer if you're still under warranty. In the mean time, buy a maintainer to at least keep it usable.

GPDRVR · 04-06-2012, 12:51 PM

Quote:

Originally Posted by ed95682

From the many previous Post I've read, it seems "normal" for the batteries to go dead after a short rest of 10+ days. Not that I'm liking this...as I've had my '06 Boxster S for 18 months and already I've replaced the batteries three (3) times! I have not been able to figure out where the electrical draw is coming from, as everything seems to be "off" when it sits for 10+ days.

A question I have would be: If you've locked the doors on the car and the battery becomes dead, then what do you do?

I know what to do if the doors are unlocked and accessing the fuse box, but if the doors are locked, how do you get access to the trunk to jump start the car? This situation hasn't happened, but I'm imagining that it can.

Hopefully you have not locked your keys in the car. And the battery is so DEAD, that no matter what is done the car will not unlock. Doors can be opened by the key, but your not able to get the front trunk open not matter what method you use. There is a stainless steel cable with a loop on it behind the passenger side head light. By levering up the light up from the bottom, ever so gently and a flash light beaming in to the side of the trunk you can see it, with a coat hanger hook, [10 - 12 inches] that cable will release the front trunk. I have heard once the cable has been located some folks put in the tow hook location for easy access later. The dealer has placed mine under the headlight, and it is still accessable without your home built coat hanger hook.
Yes my car could go a month without killing a battery, last December on 6 degree day the battery was deader than a door nail, and after killing 2 from the local parts store [at $130 they were not happy either] - bought the pricey one from the Dealer [$200] and killed that one. Then had it towed to the Dealer to replace it and they could not find any trouble and sent me home telling me 'YOU NEED TO USE A TRICKLE CHARGER' that you need to buy from PORSCHE. what a scam. and charged an hour labor. might as well have bought another dealer battery after getting that bill.

pesticidal · 04-06-2012, 02:52 PM

With all the reports of dead batteries, I'm thinking of buying a solar charger and plug it in when I'm going to leave it for a week or tow. Good idea or not?

fatmike · 04-06-2012, 07:35 PM

I had a similar issue. Parasitic draw. In my case, there is a very dim interior ambiance light that would stay on. This light goes out when the electronics go off a minute or three after you turn off the ignition. My ignition switch was bad, and the lights stayed on which killed my battery. We changed the ignition switch and magically my battery has been fine every since.

When searching for a parasitic draw, also check the lights in the front and rear trunk, sometimes the latch doesn't work properly. My mechanic said he put his kids in the trunk with a flashlight to check if the light goes out...I don't recommend that approach. Maybe take a video recording on your phone instead?