bald_joint

Hello everyone,

I've been searching, reading and testing pretty much everything we can think of, but now, I have to admit I'm clueless...

The symptoms are quite usual, as many of you may already encounter with parasitic draw : Battery goes dead (~10.6 Volts) after 7-10 days of inactivity

• My battery (700 CCA) is one year old and my tests with the battery load tester says it's good...
• With a fully charged battery (12.8 Volts) and my tests with voltmeter in between neg battery pole and cable, current flow is within specs (0.03 Amps)
• Removing fuse 11 (Cigar Lighter, Interior Lights) brings down current flow to pretty much nothing

Now, is there anything else I should be looking for... Car is parked in garage and there is nothing else that should be using electricity
I cannot trace down the exact time when this started to happen in order to be able to think of any other root cause that could be implied in this problem...
I think it may have been an intermittent problem for a short period, but now, it happens every time I leave the car unused for more than 6-7 days.

Anyone already faced this problem before... Should I be looking for leprechauns in my garage the play with my brain? ;o)

Any help would be appreciated

Thanks

divil

What happens if you charge the battery and then leave it disconnected for that same time period? It could be faulty.

dme

glove box light staying on. Had that problem with another vehicle once. 30mA isn't bad though.

Tom M'Guinn

I'm not sure I'd believe that battery load test. I've had batteries die in less than 2 years, primarily when they've been regularly left to sit for a week or more between charges. Battery tenders really do extend the life of a battery and are worth considering if you car is frequently sitting for days on end. I'd second Divil's suggestion of checking the battery over time without it connected to anything. When mine died a few weeks ago, I could charge it to the max and see 12.6 volts, only to see the volts steadily decline to 10 in a matter of hours -- all while it sat on the garage floor without anything near it. Yours may not be as dead, but checking to see how long it holds at the full charge level may tell you more than a good/bad load tester. You might also check for parasitic drain again, but leave it hooked up for half an hour or so. Some smart electronics can have internal timers that change things after time and change the current draw. It's more likely they decrease the draw after a while, but worth checking...

Droops83

Here's a copy-and-paste of a post I made last year:

Yes, this is the easiest way to isolate which circuit is draining the battery. Connect an ammeter in series with the negative battery cable, or even better, use an inductive amp clamp if you have access to one. If there are any aftermarket accessories (stereo, alarm, etc) connected to the battery positive cable or elsewhere, disconnect these first.

In almost 15 years of working on Porsches for a living, the most common batterydrain on '80s-era cars ('84+ 911s and '85.5+ 944s) is caused by faulty and/or corroded door contact switches. This does not cause the interior light to stay on (in fact it causes the interior light to not work at all in the door switch-activated position), but instead causes the power window relay to remain activated. This is because these cars are wired to enable the driver to close the windows after the ignition is switched off, but before the doors are opened (once the doors are opened, terminal 85b of the power window relay is grounded via the door contact switch, which de-activates the relay). A faulty or corroded switch will cause the relay to stay activated, which is about a 200 milliamp (0.2 amp) drain on the battery. This is very easy to verify---if you can operate the power windows with the ignition switched off and the door(s) open, you have found your issue!

When I first started at my shop as an apprentice, I was tasked with diagnosing a batterydrain on a 964. My boss (who is from Germany) knew exactly what the problem was, and gave me the factory wiring diagram manual and told me to figure it out. I had no idea about this particular power window relay arrangement, so it took me most of the day to figure it out!

Scott H

Another general hint for tracking down these kinds of draws, measure the voltage drop across fuses to isolate where the draw is coming from. Cross reference these charts to see how much current is passing through the fuse: https://www.powerprobe.com/fuse-voltage-drop-charts

Droops83

Thanks for sharing, this is my preferred method to measure parasitic drains, because you are not disturbing the circuits by pulling fuses.

However, you do need a quality multimeter such as a Fluke to accurately measure in micro-volts.

Tom M'Guinn

How low would you expect the draw to be? Mine is 19mA, but that's after I worked at eliminating unnecessary drains (alarms, radar, etc.). I could be off base, but to it seems to me if the battery is dying in a week with "only" 30mA draw, then the battery is losing its charge faster than it should. That's only 5 amps of draw in a week, which a healthy battery should be able to weather no problem, I'd think. I'd agree it's always worthwhile to eliminate unnecessary drains, but wonder if that's really the core issue here?

Droops83

I just re-read the first post.

He is measuring correct draw by disconnecting the battery and measuring the current draw by using an ammeter in series. If the door switch/window relay as I posted above is indeed the problem (I suspect it is), the stuck-on relay deactivates when the battery is disconnected, and does not re-activate until after the next time the ignition switch is cycled. This is why this particular drain us hard to chase down unless you are using my preferred non-invasive method of using an inductive amp clamp and measuring voltage drops across the fuses as posted above.

So, he is measuring a 30 mA draw after the battery circuit has been interrupted and/or the fuse is pulled, which is perfectly normal, but it is likely the ~200 mA drain of a stuck-on relay that is causing this.

bald_joint

Thanks for the idea Divil, but I've already tested this long ago and the battery did kept the charge for more than a month.

The bulb light in the glove compartment is working as it should.

I will try testing with the Positive pole instead of the Negative side to see if this change anything. I do have an aftermarket radio but I doubt this could be the issue.

Thanks for the hint Droops83, while reading your post, I did realize something that started to happen not too long ago. It didn't ring a bell at first, but now that you speak about the contact door switch that open the interior light, the warning buzzer from the relay is not always buzzing when I open the door, but the dome light do lit up! I will do more investigation on that side.

GPA951s

Keep in mind Diodes in the alternator are meant to be essentially one way valves... They get old, and "leak" it is a source of parasitic drain that often goes overlooked.

Tom M'Guinn

Got it. One thing seems clear then. Either the draw is bigger than the 30mA being seen, or the battery isn't holding power as long as it should. If the OP doesn't have an amp clamp, maybe just remove that relay and see if the battery stays charged longer? Or just cycle on the ignition with reasonably big test leads (no starter obviously). Whenever I've had a battery that lost its starch, the voltage would decrease noticeably over the course of a few hours or few days with nothing connected to it. If this one stays charged for long periods of time when disconnected, then a stealthy parasite of the type you describe sounds more likely.

p.s., of course now I want to make an inductive do-hickey that measures cumulative draw over time with everything connected, but hoping the SIP ends before I get that far down the list...

Droops83

That sounds interesting My shop's 20+ year-old Fluke 98 has a "flight recorder" mode that allows current draw via inductive clamp to be recorded overnight or over the weekend in the event of a very intermittent drain. Of course, it doesn't help to identify the source of the draw if only the battery cable is being monitored, but it does confirm if there IS a draw. We don't use it often, but it has proven helpful on a number of occasions.

Tom M'Guinn

Hey wait, I have a 20 year old Fluke 98 with amp clamp. It does that? I rarely use that one. I have a simpler Fluke I use nearly every day, but only get out the 98 for special occasions...