Impossible Battery Drain/Load-over-time problem?

[Doug B.]

Something causes the battery to run down if the car isn’t driven for 5 or 6 days, but I have measured 10.7 mA when the car is in “sleep” mode. I assumed there was going to be an obvious parasitic load, but can’t see how 10.5 mA could drain a battery to the point the electric liftgate stops working (the first item to experience problems when the battery charge is low). If the car is driven every day for 45 minutes at a time or more, I don’t have a problem with the battery running down.

This is a Porsche Cayenne SUV, 2008 model, V8. After 5 to 7 days of not driving the vehicle, the battery charge is low enough that the motorized liftgate will not work. Owner’s manual says the first thing that stops working when battery voltage is low is the lift gate motor. It takes a standard Battery Tender quite a while to fully charge the battery after it gets that low… more than 24 hours… probably in the 16 hour range, so the battery charge is definitely depleted.

This car came to us with a battery that was a little too small (H8) for the battery box in the car… apparently every battery size database in the world says it takes an H8 battery, but it doesn’t it needs an H9 that’s the same height and width, but 2-inches longer than the H8. The H9 fits the battery box (under the drivers seat) perfectly. So this car has a brand new AGM H9 battery (which is a HUGE battery, BTW, 950 CCA). The H8 battery in it had a December 2015 manufacture date so it wasn’t old, it just didn’t fit right.

To measure the draw on the batter, I put 2 ammeters on the battery…. a Fluke series Ammeter with the current flowing through the test meter leads… connected to negative battery terminal and to the removed negative battery cable. Second ammeter is a clamp-on meter, clamped around the positive battery cable. Clamp-on meter reads higher than the Fluke meter by maybe 15% to 20% but it’s there as a sanity check because what is happening CAN’T be happening…

Obviously, the whole car goes dead when I remove the negative battery cable… except the battery backup system for the alarm! (car alarms are REAL LOUD when they go off inside your garage!!! Just in case it hasn’t happened to you yet, LOL!). I timed the profile of the initial current and the gradual drop in current draw (numbers here from the Fluke meter that I trust more) as car systems wake up and go back to sleep when they aren’t used…
Initial power-up when meter leads are connected between negative cable and negative battery post – 10.5 Amps on the 10Amp Fluke Ammeter connection (I don’t know how it read more than 10A either).
After 1 minute, amps are down into the 7 Amp range, At 5 minutes Amps go down to 4. And at 10 minutes, there is a brief drop to 2.5 amps then current goes down to 00 on the Fluke’s 10A scale. I repeated the test using the 100 mA scale of the Fluke meter and after 10 minutes, I get 10.7 milliAmps.
That’s IMPOSSIBLE. 10 mA can’t mostly discharge a battery in 5 or 6 days of not driving.

Car’s Voltmeter (on the dash) reads about 12.8-12.9 volts while driving. An independent Porsche service shop says that’s good/normal/typical for this year/model and that factory Ammeter reads a little low normally.

I pulled fuses one at a time anyway to see if I could find the source of the 10.7 mA draw and came up with nothing. No one fuse drops that to zero. Some of the fuses cause a current draw temporarily after they are re-inserted, but I always wait till it drops down to 10,7 mA before pulling the next fuse.

One thing that was suggested as a possible source of the problem is the amplifier for the audio system not shutting off. So after waiting for the car to reach 10.7 mA again, I inserted the ignition key and turned it to the accessory position and turned the radio on (I had habitually been turing it off before turning the ignition off when parking the car thinking that perhaps the audio amp stayed on only if the radio was turned on when the ignition key was turned off but that made no difference compared to leaving the radio on when turning the car off. Turning on the ignition key did produce a big current draw initially, but it dropped fairly low fairly quickly even with the radio running at low volume. Turned the key off while the radio was still working (radio goes off when you remove the ignition key) to shut-down the car. After several minutes, it settled back to 10.7 mA. So I don’t think the audio amplifier is killing the battery.

One thing I’ve noticed that I have no information about is… after the car has been driven an hour or so and parked in the garage, when I connect it to the Battery Tender, the RED light on the Battery Tender illuminates indicating the battery is charging. After 1 hour to 2 hours, the green light on the Battery Tender is blinking with the RED light still lit indicating the battery is approaching fully charged. After another 30-60 minutes, the RED light goes off and the green light comes on steady indicating a fully charged battery. Is that normal for ANY car (our other car is an electric car so I can’t check that easily)?

If there is no parasitic load on the battery, what else could POSSIBLY run down the battery over 5 or 6 days of not being driven?

I should mention that we live in an area where a LOT of places we go to run errands are within 2 miles of home. So I might drive a mile, shop, open the liftgate, drive another mile (Air Con running full blast more than likely), park, shop, open the liftgate, drive another mile, park drop something off, drive another 2 miles to an appointment, etc. So I could drive 5 miles and stop/start the engine 5 times and open/close the liftgate 4 or 5 times… I could see that running down the battery over time because 5 miles of driving time isn’t enough to recharge the battery after 5 engine starts and 4 or 5 liftgate actuations (the motor closes the liftgate also, but that’s probably not a lot of current compared to opening the gate.

Anyway, my mind was blown to see the “resting” current go down to 10.7 mA after 10 minutes (that was unlocked, if you lock the car, it goes into rest/sleep mode in less than 1 minute, so we have even been locking the car while it was in the garage but that didn’t seem to make any difference. I thought SURE I would find the parasitic draw with the remove-the-fuses-one-at-a-time trick, but when the resting current hit 10.7 mA even before pulling any fuses I realized that this wasn’t going to be a normal parasitic drain problem.

Any ideas or help with the “is it normal for the battery to appear to not be fully charged to the Battery Tender after being driven for an hour?” question would be appreciated. I’m guessing this is normal behavior for a Battery Tender since it charges a battery differently than an alternator, but I want to be sure I’m not full of crap on that assumption.

Topic

[Bubba]

Measure how many volts alternator puts out when car is running? I just worked on a Porsche and they are ODD CARS!

[Richard Kirshy]

Very descriptive tr4ouble shooting.
If all your power and ground connections are clean and tight.
And considering what your current draw reading are correct

My question or thought might be:
Could your power draw be happening some hours or days after you checked it?

I did see where a vehicles alternator, when left sitting for a few days (and due to moisture/humidity ) developed a partial short.
Which killed the battery, much the same as you describe.
Took a while to track the problem down.

My suggestion:
Fully charge up your battery.
Set up your amp meter in parallel with the battery and have it where you can view it.
Let the vehicle go to “sleep” and leave the amp meter attached and see over the course of the 5 or 6 days you see any increase in current draw.

[Doug B.]

I thought about that, but if I drive the car a lot, like daily for 45 minutes or more, the battery doesn’t run down… it only runs down if the car sits unused in the garage for 4-6 days at a stretch.

[Richard Kirshy]

Exactly what I had seen.
Driving the car daily, allowed any condensation to dry out and the battery charged up, though the car was driven for longer periods.
Though in your case, with as many stop and go trips your doing, your not giving the charging system enough time to recoup the battery.
If there is a partial short developing due to moisture and/or condensation build up and with a partially discharged battery.
There is a combination for a dead battery.

[Doug B.]

I doubt condensation is an issue here. It doesn’t rain from April to late October and humidity is typically 20%-40%. Daytime highs in summer run 78-104. But there could be some odd build-up of old dust from the brushes in the alternator I suppose. If I can organize a sufficiently long… like 5-day period where I don’t drive it at all I’m definitely going to start with a fully charged battery, then connect the Battery Tender to see how long before it goes to full-green after sitting for 5 days. I have a 2000 BMW station wagon that sits in the driveway for MONTHS and the battery doesn’t die even if I just start the car half a dozen times in 4 months to move the car… only running the engine for 10 minutes at the most. And it held up to all the short trips with ZERO problems.

I’d also thought about leaving a meter connected for an extended period of time to see if the parasitic drain starts happing hours or days after the car is in “sleep” mode. Problem is, the battery is under the driver’s seat…. VERY problematic when trying to get a meter connected. And you have to measure current in series with the battery so you have to remove a post (I use negative for the obvious reasons) and all the current operating the car and charging the battery has to go through the meter. This car over-ranges the Fluke meter that only goes up to 10 Ams for a brief period when you first reconnect the battery after connecting or removing the ammeter. I would have to buy some sort of specialized ammeter that can pass however much current is required to start the engine AND still read in milliAmps for seeing what happens when the car sits for hours or days (to see if the 10.5 mA “sleep” draw changes). It would be interesting to see what the car is doing in the current realm while driving… it just can’t happen with the 2 meters I have… the Fluke only goes to 10 Amps. The clamp-on meter has 100, 20, and 2 Amp settings, but it’s a clamp-on meter so it’s impossible to read with the driver’s seat down… because the battery is under the driver’s seat. So I need an auto-ranging Ammeter I can leave connected permanently… something that can take max current that will ever come out of or go into the battery… and that meter should have negative, 0, and positive Amps so I can see if the battery is being drained, charged, or neither at any given point in time… driving or parked. I have NO idea what the maximum current is… probably starting the engine puts the most draw on the battery. So not sure where to look for an ammeter like that… beefy enough to handle all the starting current, but sensitive enough to measure milliAmps when the car is “sleeping”. It would also help if I could connect a computer and capture readings every minute or two so I could plot the results on a chart. Maybe I should be looking for a USB Ammeter??? (half joking, there may very well BE such a thing). Just did some quick reconnaissance and came up with NOTHING that could hadle 12volts and up to 100 Amps… most of the shunts for ammeters that are rated for 100A can work at no more than 75 mV!!!! A shunt that can handle 12-volts and 100 Amps (headroom is always good) would be huge and that would have to be installed between the negative battery terminal and the negative battery cable and you would connect the Ammeter across that shunt to measure current (via voltage drop across the shunt presumably). If anyone has any ideas where to look for a device that will do this, please let me know… willing to try almost anything at this point. Has to be a solvable problem here somewhere.

Also – anybody know of a reference that shows battery life with various loads on the battery (like 10 mA, 1 A, 2 A, 4 A, 7 A, 10A, etc.)? Not having any luck finding anything like that either.

[Richard Kirshy]

For the range and resolution your requiring…
You might consider looking for a automotive test scope with an appropriate amp probe.

Or, as you mentioned you have a FLUKE meter.
But you did not mention which model
You may have this option:
http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/accesscurrentclamp

You may need to get creative in how you attach it, but there are always possibilities

Another thought to be considered.
You state you replaced the vehicle battery.
I suggest you have it fully tested ( load and capacity ) it would not be the first time a new battery has failed.

Here is some reading that might prove useful:
https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html#8
As to:
Also – anybody know of a reference that shows battery life with various loads on the battery (like 10 mA, 1 A, 2 A, 4 A, 7 A, 10A, etc.)?
Knowing the (RC) and (AH) A little math and you can answer your own question.
This is covered in the above reading

[John]

Could you use just a simple ammeter like the gauge in the dashboard type, the kind you’d buy at Autozone, between the alternator output lead and the battery? They’re not super accurate but good enough to see a big drain. See if the drain is happening on that side of the circuit? With most vehicles the positive side of the battery only runs to the alternator (thin cable) and the starter (heavy cable) so any leech in the electrical system should be seen on that lead. Watch it for something significant whenever you get bored and go look?

[Doug B.]

The Flule meter is probably 20 years old, but measuring amps hasn’t changed in that time. 😛

The problem with clamp-on devices for measuring current is that to work well, they have to have the cable being measured held in the center of the clamp and the circuit being measured should be stationary since the earth’s magnetic field changes the readings. If the clamp moves while taking a reading, that also changes the reading… and the clamp can only go around 1 wire (positive or negative, but not both at the same time). And the meter will time-out and turn itself off after 5 minutes too… already happened to me often while making the measurements I’ve already done. I hadn’t seen a clamp on the end of test leads before though… that could turn out to be handy later if the clamp becomes the only way to see what is going on right at the battery with the battery being located, inconveniently, under the driver’s seat. I’ll give up some accuracy, but may get enough info… I’d have to see about running the leads outside the door though, when the car is in “sleep” mode, opening a door immediately wakes it up.

Yes, I did replace the original battery for 2 reasons…. the original was 2-inches too short and did not fit the retaining brackets in the battery box AND I wanted to see if another battery behaved the same way. The battery in the car had a manufacture date of 12-2015 so it was a new wet (lead-acid) battery. The replacement was made in May 2016 and is an AGM (absorbed glass mat) filled with gel instead of liquid acid. The original battery was 900 CCA, the replacement battery is 950 CCA (battery capacity spec is “740 CCA or higher”).. Both batteries act the same so no need to replace the battery again. I fully charged the new battery on a Battery Tender before installing it… the store said it was fully charged, but I don’t think it had a full deep charge at that point, it took the Battery Tender about 22 hours to get the new battery to a fully charged state..

Will take a look at the battery info link shortly… thanks for that!

Now I’m beginning to question the alternator… have to see what I can find out about the design… whether it is 1 phase, 2 phase or 3 phase, If it is 3-phase and it “lost” 1 phase it could be undercharging the battery, even on longer drives and that could build-up quickly with a couple of weeks of short trips. If it is a 1-phase design and you lose 1 phase… you get NADA out of the alternator so that’s definitely NOT my problem. With a 2-phase alternator, losing 1 phase is pretty severe… the issue might be more severe than what I’m having, but not sure. But should be some way to test this. I do have an oscilloscope so I could look at the AC coming out of the alternator if there are connectors accessible before the rectifier(s)–not always available though.

[Doug B.]

[quote=”Johnny Stang” post=173187]Could you use just a simple ammeter like the gauge in the dashboard type, the kind you’d buy at Autozone, between the alternator output lead and the battery? They’re not super accurate but good enough to see a big drain. See if the drain is happening on that side of the circuit? With most vehicles the positive side of the battery only runs to the alternator (thin cable) and the starter (heavy cable) so any leech in the electrical system should be seen on that lead. Watch it for something significant whenever you get bored and go look?[/quote]

I think I need something with more accuracy in case the drain on the battery is in the 50 mA to 2 A range… so that really requires a digital display that just moves the decimal point depending on the Amps being drawn so you never have to adjust the range, you just have to pay attention to the location of the decimal point. A conventional analog ammeter with a needle moving left or right to indicate charge or discharge won’t necessarily tall enough about what’s going on. It MIGHT, but don’t want to gamble on being mislead or not getting a useful result. So probably need that sort of functionality but with a self-ranging digital dieplay and maybe something that stays on all the time so even at night I could go out to the garage with a flashlight and read the meter without opening a door.

[Richard Kirshy]

Ok,
Lets put things in a little perspective here.
To begin with:
I wouldn’t worried too much about the battery CCA
You state 740 or higher required.
What is important is RC (reserve capacity)
That will determine how long the battery can last with a draw on it.

Next item:
Hooking up your meter.
Lets get real here..
Your issue is that your battery is draining over the course of 5 – 6 days.
So your looking at most a couple of amps if that.
Your not going to see any type of high current draw
So your testing is going to have to be done with the vehicle parked for at least that long.
Simple way:
You’ll need 4 test leads.

This should explain the setup

Attachments:

• Amptest-2-3.png
• Amptest-2-3-4.png

[Rob]

Im willing to bet you that the backup battory is drowing a lot more power then you think it is…. if the battory is like over 3-5 years its t its end of life and will draw more power…. and how your actually measure it will not show your true draw that it is drawing… I have to go for a little bit I will come back and explain why your orginal testing is bad if the backup battory is the problem… and why you will not see that in your first test trying to find the draw that is drawing the main power and why it is giving you a fauls reading’s

[Doug B.]

That would work… except if the draw starts hours or days later and isn’t always there, I’d have to be there to see it. Which makes connecting a current measuring device to a computer that could log and plot current data over time would be the best solution if I can figure out how to do it without spending a ton of money. I figured when I searched for USB Ammeter I’d find all KINDS of results but all I got was little meters you plug into a USB port to measure current flowing through the port… not from some outboard device you want to measure… MUST be out there somewhere. There are current and voltage monitors that run constantly for solar panels for example… just need something that works in the operating range of a car.

[Doug B.]

[quote=”Rob781″ post=173210]Im willing to bet you that the backup battory is drowing a lot more power then you think it is…. if the battory is like over 3-5 years its t its end of life and will draw more power…. and how your actually measure it will not show your true draw that it is drawing… I have to go for a little bit I will come back and explain why your orginal testing is bad if the backup battory is the problem… and why you will not see that in your first test trying to find the draw that is drawing the main power and why it is giving you a fauls reading’s[/quote]

OK, that’s promising. Never thought the alarm backup battery could be the culprit here… I have NO DOUBT that it is now 8 years old and is original to the car. I have NO idea where it is located either…. probably NOT in an easily accessible location since you wouldn’t want the crooks to have easy access to disconnecting it… so not looking forward to possibly having to dig into the guts to replace the alarm system backup battery. While waiting for your follow-up, I’ll see if I can find out where the alarm backup battery is located. May require purchasing service manual and electrical diagrams… not too costly as downloads of non-Porsche documentation, but same info used by outfit that provides shop manuals to independent shops. Seems pretty accurate in the bits I’ve seen. There is a second covered “box” next to the big battery under the drivers seat though… big enough to hold a battery as large as maybe 2/3 of a brick.

[Richard Kirshy]

I would think when or if the draw occurs, it is persistent.
If you were measuring 10Ma draw when the vehicle is asleep, something is either being commanded on over time or
a partial short is occurring.
BTW
Correct voltage at rest on a good battery should be 12.6V
Common voltage output of the alternator is somewhere between 1 volt over resting voltage to 14.5V.
Unless you have some exotic charging system or massive electrical options 14.8 is the highest safe charge rate.

[Richard Kirshy]

Hmmmm, alarm back up battery.
I missed that little blip.
I would be curious to know if that backup battery is being supplied by the alternator on a separate charge circuit,
or a separate charging circuit off the primary battery.

That is one of the most frightening wiring diagram :ohmy:
I only managed to see a couple of pages.
Wonder now if disconnecting the back up battery will prevent your issue.

[Author]

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