Yet Another Weird Battery Drain Thread!

[masbury]

The Car: 1998 750iL
The Problem: Battery slowly loses voltage

I have tested for any drain issues caused by the car not going to sleep and came up with exactly 50ma. After all the reading I've done (Thanks Timm), that seems to be the correct drain after going to sleep, yet the battery will still slowly drop voltage. The battery is 1 year old. The tender has been tested and puts out 14vdc. The alternator puts out 14vdc+ when driving. I'm kinda stumped here. On paper, this should not happen, but then there's real life.

I would actually appreciate any weird off-the-wall suggestions as I am stumped.

Grateful as ever for this forum and the brilliant minds that populate this place.

Mike

[rslifkin]

Just to confirm that the issue is the car and not the battery, try charging the battery fully (let the charger float the battery for at least 6 hours after it says it's full), then disconnect the charger. Leave the interior lights on for 1 - 2 minutes to drain off the surface charge on the battery, then disconnect the battery. Check the voltage once or twice a day for a few days and see what it does. It shouldn't drop below 12.6 or so (assuming it was really 100% charged at the start of the test).

[BimmerFlyer]

I am actually in the process myself of trouble shooting a”not going to sleep all the time” issue on my ‘97 740il..
not having a whole lot of luck yet.. but I did find that my “sleep mode” draw is actually only about 25 mA... so not sure if your 50 mA id indeed correct or not.... however, in research this subject I did indeed find that everyone considers anything below 50 mA to be acceptable...
The search continues.. what a pain in the —-.
Pete

[masbury]

Amen brother...

I will tackle your suggestion.

Thanks,

Mike

[masbury]

rslifkin;

Took your advice and disconnected the battery and checked voltage everyday for a week. No change, no drop, all is good.

So, reconnected battery through meter. About a 4-5 amp drain, slowly decreasing as system shut off. At the 16 minute mark the trunk lights went out and I then read this on the meter. Please tell me I'm reading 40 milliamps.

20190503_092635.jpg 20190503_092559[1].jpg

The pics are in two different scales (just to cover my ass).

If it is 40 milliamps, then that should be within spec. If so, what could be causing the drain. The thought has crossed my mind that somehow the tender is freaking out, so am going to try a different one, but other than that, I'm completely stumped.

Any other suggestions would be most helpful.

Thanks,

Mike

[Timm]

Yes, that's 40mA - and you haven't got any battery drain. If your battery is losing charge then it's dead!

[rslifkin]

I'll agree that it's not enough drain to kill the battery any bit quickly. How long a time are you noticing the drain over? It's possible that it's an intermittent problem I guess.

[masbury]

I don't let it go dead, but it will lose .2vdc (12.46vdc to 12.25vdc) over a 3 day period. Doesn't seem like much, but if I let it, it will drop below 12.5vdc, which is as far down the totem pole as I would like to get.

I have checked the tender and it (appears) to be working correctly, but maybe it has a problem in it's sensor circuit, in that it doesn't see a voltage drop until it's too late, or not at all. When I hook it up to my meter, I get voltage reading up to 14.6vdc.

Thoughts?

Thank you gentlemen,
Mike

[rslifkin]

Wait a second... It's losing that much voltage while connected to a tender? If that's the case, the tender has an issue. How fast does it lose voltage without the tender hooked up?

[Timm]

It's worth saying that a battery fresh from a charger will not have a terminal voltage that reflects the state of charge - it will measure higher than its SOC due to the surface charge. To read a useful battery terminal voltage you have to remove the surface charge. This is done by switching the ignition ON but not starting the engine and leave the headlights switched ON for 10 minutes.

Once you have done that you will have a terminal voltage that can be referenced to the SOC table:

[rslifkin]

FWIW, open circuit voltage does vary a bit more than you'd expect between batteries. I've seen some AGMs that hold 13.1v or a little more for months after being taken off a charger. And some batteries (AGM, wet and gel) where 12.6 is really as full as it gets.

[1986series6]

I also have a draw I can't find. i've done all the tests with TIMMS help.
My meter reads .01 to .02 so I just decided to cheat with a collector type negative battery
disconnect switch. Not my DD so I connect when I want to drive the 7.
I've left the car untouched for as long as 3 to 4 weeks, connect the switch and it starts and runs with no problems.
I'm just done with trying to figure it out. 98 740i

[masbury]

So, as an experiment, I swapped out battery tenders. The minute I connected the 2nd tender, it's charge light went on. The tender I removed was apparently not charging as it's charge light was not lit. It's possible the 1st tender got "stupid" and didn't know when to begin charging. I'm checking voltage on a daily basis now that the 2nd tender is installed and will report back in a few days with findings.

What a PITA!

Thanks everyone,
Mike

P.S. 1986series6 - I feel you're pain!

[rslifkin]

If the first tender wasn't behaving correctly, it's possible it was actually drawing a little bit of power from the battery. If you want to confirm the car has no issues, let it sit unplugged for a few days (after getting the battery topped off) and monitor voltage to see if it drops slower than it did with the first tender.

[masbury]

So with the new tender it's still losing voltage. Dropped .5v in 3 days. I am now considering Timm's thoughtful suggestion "Yes, that's 40mA - and you haven't got any battery drain. If your battery is losing charge then it's dead!".

The battery is approximately a year old, but (and that's a big but). Got it at Walmart before I figured out about "Blems" at Interstate, which are way cheaper. So, do I take this POS back to Walmart (it should be under warranty) and exchange it for another POS, or junk it, use it as an emergency spare and just go get an Interstate? Or (another possibility), return it to Walmart, get my money back, go buy the Interstate and put money back in my pocket?

In this case, opinions are greatly appreciated...

Mike

[BimmerFlyer]

So with the new tender it's still losing voltage. Dropped .5v in 3 days. I am now considering Timm's thoughtful suggestion "Yes, that's 40mA - and you haven't got any battery drain. If your battery is losing charge then it's dead!".

The battery is approximately a year old, but (and that's a big but). Got it at Walmart before I figured out about "Blems" at Interstate, which are way cheaper. So, do I take this POS back to Walmart (it should be under warranty) and exchange it for another POS, or junk it, use it as an emergency spare and just go get an Interstate? Or (another possibility), return it to Walmart, get my money back, go buy the Interstate and put money back in my pocket?

In this case, opinions are greatly appreciated...

Mike

mine was an Interstate as well, 4 years old and only would take a surface charge, IE behave exactly like yours does...load tested and was junk..... Batteries are just not made like they were used too, even compared couple of years ago... ended up buying another Interstate for $225, because that was all that is around... not sure if anyone makes a better battery or not..there are really only a couple of battery manufacturers left, that just slap whoever’s label on it...I am not sure what is killing them so quick, but they sure don’t last..
Pete

[Timm]

Batteries tend not to be junk - but you can kill any battery in months if the state-of-charge is low - if you want to keep a battery at 0% SOC then get a AGM!

[agentrnge]

I was chasing issues like this in my e39. At first I had solidly identified a few draining gremlins, resolved those, batteries still fading over a week or so, replaced the battery, knowing that the chronic drain/deep cycle would have toasted it. Would still only get 1-2 years out of a battery. Kept replacing them. Went with AGMs from Autozone everytime thinking AGMs would hold up better. No such luck, even with no drain I was never getting solid perf out of AGMs.

I went back to standard batteries and they have been holding up much better. Maybe I just got super unlucky with batteries until I got a good one. Had a standard battery in my e39 up until I sold it, and also now in my e38. The e38 can sit for a week or two and not drop much at all. I would use a tender/charger to top it up if it sits longer than a week, but whenever I throw the charger on its already in a healthy state like 12.5-12.6v. My AGMs would test way low, like 11.6 low all the time after sitting for just a couple days, with no observed drain. It would also start up fine without hesitation. Dunno. I cant find it know but read at one point that AGMs vs standard lead acid batteries require slightly different charge voltages to be really happy.

[BimmerFlyer]

Not to sound crazy, but one of the things I have seen with mine in the process of troubleshooting a random battery drain, was, the car would literally wake itself up from sleepmode and put itself back to sleep again 16 minutes later... since I was trying to find a problem, I was watching it like a hawk and just happen to catch it in the act.. A car waking itself up a couple of times a hour for a couple of days would also be a possibility for what seems to be a bad battery...AND, even tho people say it it not possible, I have seen a battery charger waking up the car when the voltage spike hit the system...some interaction between that could also be an issue..
Pete

[masbury]

Full disclosure. About a month ago, I readied the car to drive - disconnected tender, got in, didn't notice there were no interior lights, turned the key and nothing, nada, doodly-squat. Checked the battery, it was 9.6v. Charged it for 3 days @ 2amps and brought it back to 12.6v.

My instincts kind of agree with Timm's. This thing may be toast. Some batteries may still be functional after a total melt-down, but probably not the "Walmart Special". Leaning toward the "replace" train of thought.

Not as an excuse, but having so many whiney cars, I sometimes lose track of who's doing what. My E32 750i, had a weird battery drain-down issue which I resolved by removing the aftermarket amplifier and trashed wiring and purchasing a new battery. Somehow, I forgot the E38 was having a similar issue until the battery went dead. Then the light went on, which is what triggered the original post! Also, in the last month, I have put brand new batteries in 4 other cars. One in the E32 750i, two in the E31 850, one in the 2000 Mercedes SL500 and one in the '67 Buick Riviera. That's 5 batteries in less than a month. I could have bought another car for what I spent on batteries!

Kidding...

Looks like I'm heading to Interstate for yet another H8 blem.

Thank you for all your ideas, suggestions, thoughts and sharing in the mutual-misery society meetings about mystery battery drains.

If any other weird crap comes up after the new battery, I'll jump in here again.

Regards and thanks,

Mike