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Old 02-18-2020, 07:55 AM   #1
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Battery Draining Every Two Weeks

Hi Boxster Friends,

I've got a 2001 Boxster S with 139,000KM on the clock (approximately 86,370 miles.) This is my second year of ownership of the Boxster and naturally, second winter with it. Below are some general details for consideration:

Location: Toronto, ON (Canada)
Storage Location: Underground condo parking (not heated)
Battery Make/Model: Interstate MTP-94R H7 (replaced August 2019)
Connected to Trickle Charger: No - Unable to due to lack of electrical outlets and I believe local by-laws do not allow for electrical outlets to be installed in the underground parking lot
Battery history: Replaced with a brand new Interstate battery (I forget exactly the model number, but equivalent factory size) in August of 2019. The previous battery no longer held a charge and was aftermarket.
Alternator: Checked and validated by three shops - No issues with charging system.

Symptoms/Issue: I don't drive my Boxster a whole lot throughout the winter but will attempt to take it out every two weeks to keep her running and to ensure everything is okay.

I know that the car will go into a "sleep" mode after sitting for 5 - 7 days to conserve the battery, but every two weeks, I'll be able to wake it up, try to start the car, but not enough battery to actually start the car; I'd have to jump start it almost every time. I would be lucky to be able to open up the front trunk with what's left. It's been pretty cold lately in the winter, about -5C to +5C / 25F to 41F. I would like to believe that the weather isn't killing the battery here.

I haven't begun diagnosing the issue yet, but any leads or recommendations to check what's draining the battery? I did find a few threads about using a voltmeter to measure the voltage of the battery, and removing fuses one by one to determine if there is a drop in voltage, and narrow down from there. There was also another thread (which I cannot find for the life of me) about some connection point in the engine bay where the starter and/or alternator connect, and possibly being a culprit. Any leads appreciated. Thanks!

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Old 02-18-2020, 08:12 AM   #2
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As long as the car is locked, it should not be draining the battery like that in two weeks. I also have an interstate battery and have not had any issue starting up in the winter (20-40 F), even after 4+ weeks without a battery maintainer. You are going to want to check the voltage as you describe. I would start with anything plugged into the cigarette lighter, wired into the always on 12V power under the center console, or that is aftermarket like a headunit, amp, etc.
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Old 02-18-2020, 08:20 AM   #3
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As far as I know, there is nothing that is hard wired into the always-on 12V under the console, or anything aftermarket (but you never know!) The only thing that was ever replaced was the alarm unit / immobilizer because the previous owner left the top down and it rained, causing the immobilizer to be water damaged. It was replaced and re-coded by a Porsche dealership. Other than that, I'd have to get my hands dirty to figure this one out. Thanks!
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Old 02-18-2020, 08:23 AM   #4
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Did you verify the Battery was properly filled with electrolyte in all the cells ?
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Old 02-18-2020, 08:27 AM   #5
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Quote:
Originally Posted by BYprodriver View Post
Did you verify the Battery was properly filled with electrolyte in all the cells ?
Good question - The honest answer is no. I trust that my independent Porsche shop would have done this. Battery in question is an Interstate MTP-94R H7. I'm not sure you can fill it with electrolyte. (Someone correct me if I am wrong.)
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Old 02-18-2020, 08:41 AM   #6
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Looks like it's having a parasitic drain. Here are a couple decent videos on how to test:

https://www.youtube.com/watch?v=lRcj1fQcWwU

https://www.youtube.com/watch?v=2Y8t5hIFtAk
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Old 02-18-2020, 09:55 AM   #7
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Thanks for the videos - they were great!

I suspected a parasitic drain, so I'll have to figure out what it is by going through this process.
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Old 02-18-2020, 10:12 AM   #8
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You're welcome and good luck!
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Old 02-18-2020, 11:34 AM   #9
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Here is a link to another thread on the subject. This may or may not help, but it has helped me quite a bit. I was having similar issues as you, but not anymore.

http://986forum.com/forums/boxster-general-discussions/71827-parasitic-battery-drain-solved.html
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Old 02-18-2020, 11:56 AM   #10
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Interesting - I'll have to try that later tonight. Thanks for that.
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Old 02-19-2020, 11:20 AM   #11
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1.5~2 month would be about right, had that quite a few time. 2 weeks sounds quite short for a '19 batt though.. most likely parasitic or faulty cell.

Few tutorials on how to debug parasitic drain(s) on YT, e.g. using a dmm and pulling fuses. I'd rule that out before coming to a conclusion that the battery is faulty and needs changing.

Far more boxstech savvy members here may know the exact constant drain figure but I believe 50~100mA drain is considered normal when parked/locked.
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Old 02-20-2020, 10:48 AM   #12
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There is a list of parasitic drains here. Page down about two pages and lots of detail on draw versus time and even the draw from individual items.

Also check the battery terminal to cable connections are clean and tight.

My first approach is voltage at 3k RPM. Voltage after 1 hour from shut off. Voltage after 24 hours. Don't be afraid to load test the battery.

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Old 02-20-2020, 11:14 AM   #13
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Quote:
Originally Posted by mikefocke View Post
There is a list of parasitic drains here. Page down about two pages and lots of detail on draw versus time and even the draw from individual items.

Also check the battery terminal to cable connections are clean and tight.

My first approach is voltage at 3k RPM. Voltage after 1 hour from shut off. Voltage after 24 hours. Don't be afraid to load test the battery.
Good advice.

My Bosch battery is 2.5 years old. Twice in one month... ~5-6 days between starts... battery was dead. Took it to AZ... load tested it: Good battery.

I had repaired some wires connected to the + cable... and tightened everything up... after the first failure. The second time, after recharging the battery... took it back to AZ: Good, again. Bought the $3 post cleaner. Cleaned everything up.

2 weeks later my voltage LED is reading ~14V.

All back to normal.
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Old 02-22-2020, 02:57 PM   #14
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Hi folks,

Just an update - I went to fire up the car today and low and behold, the battery was dead (no interior lights, no dash lights - nothing.)

Except for that darned stereo LED light flashing. I had to open the front hood using jumper cables connected to my trusty Toyota Corolla, and jump started the Boxster within seconds of connecting it.

I followed the instructions provided by Troy.Boxster on how to disable the LED prior to driving out o my condo parking lot, and went for a good drive for an hour and a bit. I'll report back in a few days or next week to see whether this has changed anything.

I forgot to ask my colleague to borrow his volt meter, so I'll try again next week, but I've always suspected that it could be the radio. Every time I turn on the radio, I hear this high pitched/metallic (almost electrical) PING! sound. Grrrr!

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