Alternator, battery, or ground issue?

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13.8 v with the engine running is what I see with a dvom on a 5 year old battery.
I had the battery load tested and it is 200cca down. 25% less than a new one.
13.3 is ok within the time span you allowed.
It sounds like the alternator is good, and the battery is good.
It still looks to me that something is causing a battery drain.

Another thing to look into:
With the car running, trunk lid up, squeeze and tug gently on the short span of insulated harness that runs down into the body from the trunk lid.
look for odd electrical behavior from lights, window mechanism, instrument cluster, while you faff with the harness.
Repeat with the engine off.
I've seen starting issues,failure of power window, odd behavior from the instument cluster, on the E30,E36, and Mercedes models, that were traced to a short in the harness from the trunk lid. The short is caused by the fatigue of the wiring at the hinge.

[lemoose]

13.8 v with the engine running is what I see with a dvom on a 5 year old battery.
I had the battery load tested and it is 200cca down. 25% less than a new one.
13.3 is ok within the time span you allowed.
It sounds like the alternator is good, and the battery is good.
It still looks to me that something is causing a battery drain.

Another thing to look into:
With the car running, trunk lid up, squeeze and tug gently on the short span of insulated harness that runs down into the body from the trunk lid.
look for odd electrical behavior from lights, window mechanism, instrument cluster, while you faff with the harness.
Repeat with the engine off.
I've seen starting issues,failure of power window, odd behavior from the instument cluster, on the E30,E36, and Mercedes models, that were traced to a short in the harness from the trunk lid. The short is caused by the fatigue of the wiring at the hinge.

But this is a brand new battery- this isnt some sort of red flag? I tried wiggling that harness with no luck

[sapote]

alright got back from vacation and got the multimeter in. i guess its time to start pulling fuses?

1. car was dead upon returning and I had to jump it. drove it around for about 15 miles- turned the car off and waited an hour. battery measured at 12.33
2. cranked the engine and voltmeter read 13.8 at the battery
3. turned the car off after about 5 minutes, removed key from ignition. reading was 12.47

1. 15 miles driving is not to fully charge a dead battery. You need a charger -- minimum 5A and charge it overnight or 12 hours.
2. You meant ran the engine? 13.8V is OK at the battery. At full charged it will be a little higher.
3. 12.47V is low, and no surprise, bc the batt is not fully charged.

I don't use ordinary charger, but a 10A max DC power supply. If I don't drive a lot then on weekend I connect it to the fender posts and set it to 14v, 6A max, and one hour later lower to 13.5v and let it charge (top off) overnight. Fully charged batt should be higher than 12.6V after disconnected the charger for 10 minutes.

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I understand that you have a new battery.
The charging performance, if it retained its charge is acceptable, but only on par with my 5 yo unit.
You have had it under alternator charge for around 2 hours of driving which should make the battery happy..
That drive time should have stabilised the charge.
Can you get the battery load tested again? To rule out a dead cell?
Otherwise it could still be draining.
That 2 hour drive should have satisfied the charging requirements.

[lemoose]

Sapote, what type of test should I do after the battery is fully charged?

I understand that you have a new battery.
The charging performance, if it retained its charge is acceptable, but only on par with my 5 yo unit.
You have had it under alternator charge for around 2 hours of driving which should make the battery happy..
That drive time should have stabilised the charge.
Can you get the battery load tested again? To rule out a dead cell?
Otherwise it could still be draining.
That 2 hour drive should have satisfied the charging requirements.

I never got the battery load tested. I assume youre referring to the same load test I can get done at the parts store?

[sapote]

Sapote, what type of test should I do after the battery is fully charged?

1) find out if the "new" battery is damaged or not: Fully charged it overnight (not with small chargers with 1A or so, these are only good for trickle charge to top off), disconnect the charger and let the batt rest with no load (don't open doors or trunk or turn on the ignition key, etc.) for 10 - 15 minutes, then measure voltage at batt post (should be higher than 12.6v). Next, run engine at idle, wait for 3 minutes then measure battery voltage (it should be close to 14v).

2) load test: turn on the ignition (but not start the engine) and turn on the headlights (ignition on + lights = 7A + 15A = 22A is my guess) for 5 minutes, then turn all off, wait 1 minute for batt to recover, then measure the batt voltage. It should not drop below 11.2v

3) connect the charger to fully charge up the batt for 30 minutes.

If you want to find out if there is a big leaking current on the car, leave it alone for 2 or 3 days with the front hood opened enough not to trigger the SMG hood switches. Open the hood and measure battery voltage at the fender jump post to engine metal. It should not fall below 12.5v

[lemoose]

1) find out if the "new" battery is damaged or not: Fully charged it overnight (not with small chargers with 1A or so, these are only good for trickle charge to top off), disconnect the charger and let the batt rest with no load (don't open doors or trunk or turn on the ignition key, etc.) for 10 - 15 minutes, then measure voltage at batt post (should be higher than 12.6v). Next, run engine at idle, wait for 3 minutes then measure battery voltage (it should be close to 14v).

2) load test: turn on the ignition (but not start the engine) and turn on the headlights (ignition on + lights = 7A + 15A = 22A is my guess) for 5 minutes, then turn all off, wait 1 minute for batt to recover, then measure the batt voltage. It should not drop below 11.2v

3) connect the charger to fully charge up the batt for 30 minutes.

If you want to find out if there is a big leaking current on the car, leave it alone for 2 or 3 days with the front hood opened enough not to trigger the SMG hood switches. Open the hood and measure battery voltage at the fender jump post to engine metal. It should not fall below 12.5v

i think we may be on to something. so the hood has been difficult to close lately- either the hook on the hood, or the switch latch dont catch right. is it possible that this might be at play?

[sapote]

If you don't hear the SMG pump priming by itself, then it should not be related issued, but don't let the hood pops up and smash the windshield at 60 mph.

[lemoose]

If you don't hear the SMG pump priming by itself, then it should not be related issued, but don't let the hood pops up and smash the windshield at 60 mph.

Hmmm maybe not then… my car was SMG but was converted to manual

[lemoose]

1) find out if the "new" battery is damaged or not: Fully charged it overnight (not with small chargers with 1A or so, these are only good for trickle charge to top off), disconnect the charger and let the batt rest with no load (don't open doors or trunk or turn on the ignition key, etc.) for 10 - 15 minutes, then measure voltage at batt post (should be higher than 12.6v). Next, run engine at idle, wait for 3 minutes then measure battery voltage (it should be close to 14v).

2) load test: turn on the ignition (but not start the engine) and turn on the headlights (ignition on + lights = 7A + 15A = 22A is my guess) for 5 minutes, then turn all off, wait 1 minute for batt to recover, then measure the batt voltage. It should not drop below 11.2v

3) connect the charger to fully charge up the batt for 30 minutes.

If you want to find out if there is a big leaking current on the car, leave it alone for 2 or 3 days with the front hood opened enough not to trigger the SMG hood switches. Open the hood and measure battery voltage at the fender jump post to engine metal. It should not fall below 12.5v

Did the above and the battery performed fine. Went to the parts store and got it tested just to be sure and they found the battery to be fine as well.

[sapote]

Did the above and the battery performed fine. Went to the parts store and got it tested just to be sure and they found the battery to be fine as well.

Including this? "If you want to find out if there is a big leaking current on the car, leave it alone for 2 or 3 days with the front hood opened enough not to trigger the SMG hood switches. Open the hood and measure battery voltage at the fender jump post to engine metal. It should not fall below 12.5v"

If you can compress the 2 days time in a few hours then everything is good, but unfortunately energy leaking cannot be compressed in this fashion

[lemoose]

Including this? "If you want to find out if there is a big leaking current on the car, leave it alone for 2 or 3 days with the front hood opened enough not to trigger the SMG hood switches. Open the hood and measure battery voltage at the fender jump post to engine metal. It should not fall below 12.5v"

If you can compress the 2 days time in a few hours then everything is good, but unfortunately energy leaking cannot be compressed in this fashion

Lol i meant 1,2,3 but ill get on it

[lemoose]

Parasitic drain from the driver inflatable bolster valve pack. Shoulda known.

When I bought the car in 2016, they had to jump it at the lot before I could test drive it. Never gave it much thought since I had imagined it was probably sitting for a while. In any case, one of the first things I noticed that didn't work was the bolster adjustment. Probably within my first week of ownership I took the seat back out to inspect the problem. Now I remember that the valve pack was hot as hell so after finding that the part was like $400, i decided to just leave it as is- but I disconnected it. In the process, I broke the holes in the seat back which resulted in the right side of the seat back separating and sagging from the rest of the seat. It mildly annoyed me for years until a couple months back I bought a replacement seat back cover and I once again encountered the valve pack. I figured what the hell may as well plug it back in and just not use it- having completely forgotten how hot I found it last time.

So, fast forward to today as I'm removing fuses and monitoring power draw I pull fuse 65 and voila- the multimeter goes from .55 amps to .05. Everything immediately clicked in my head. I remove the rear seat cover and sure enough, the valve pack is too hot to even touch.

[sapote]

I figured what the hell may as well plug it back in and just not use it- having completely forgotten how hot I found it last time.

Luckily I didn't see on the news about man roasted on his M3 seat. I have a good laugh on Friday. Well done.

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Glad you got it sorted.