Low voltage after new battery

[Helmsman]

Originally Posted by Redd

How do I check? Cos right now I have zero errors or symptoms.

Have Carly? If so you have a check point of actual alternator current output which would be nice to confirm as a start. Should hover around 30-40 amps during normal conditions.

[Scharbag]

Originally Posted by pbonsalb

It goes from the oil pan to frame rail under the header collector on the driver’s side. They can rot out. Give it a tug.

This made me laugh.

I am such a child.

[Redd]

Originally Posted by Helmsman

Have Carly? If so you have a check point of actual alternator current output which would be nice to confirm as a start. Should hover around 30-40 amps during normal conditions.

I just ordered ISTA+. Will check this first thing the cable gets here. Thanks!

[Redd]

Update - After slightly over 1 month and 1000km, voltages are back up to 13.5-14V regularly. CTEK shows the battery is charging up to 100%.

I didn't do anything or change anything. Seems like the problem just fixed itself, or it's normal after a new battery registration.

[dpaul]

Originally Posted by Redd

Update - After slightly over 1 month and 1000km, voltages are back up to 13.5-14V regularly. CTEK shows the battery is charging up to 100%.

I didn't do anything or change anything. Seems like the problem just fixed itself, or it's normal after a new battery registration.

Registration is irrelevant. Hopefully the problem will not return.

[Helmsman]

Originally Posted by Redd

Update - After slightly over 1 month and 1000km, voltages are back up to 13.5-14V regularly. CTEK shows the battery is charging up to 100%.

I didn't do anything or change anything. Seems like the problem just fixed itself, or it's normal after a new battery registration.

Haha, always exciting to return to an old thread and find I thought I had it all figured out.

Well my turn - Replaced the battery. Once coding and register was confirmed (using Bimmergeek), I all of a sudden get increased charge voltage at 14.8V vs 14.3 isch with the worn out battery. Temperature has fallen to below 0 which apparently is being compensated by the ECU, but reading this thread an old battery apparently should be compensated with higher charge voltage puzzles me. I also went from AGM to flooded which again should lower the voltage if anything.
Yours has been fine since replacement or noticed any further odd behaviour Redd?

[Vuu]

Originally Posted by Helmsman

Haha, always exciting to return to an old thread and find I thought I had it all figured out.

Well my turn - Replaced the battery. Once coding and register was confirmed (using Bimmergeek), I all of a sudden get increased charge voltage at 14.8V vs 14.3 isch with the worn out battery. Temperature has fallen to below 0 which apparently is being compensated by the ECU, but reading this thread an old battery apparently should be compensated with higher charge voltage puzzles me. I also went from AGM to flooded which again should lower the voltage if anything.
Yours has been fine since replacement or noticed any further odd behaviour Redd?

In the same boat as both of you, except I live in SoCal.

Replaced the battery and get the discharged warning. Car has been on a tender ever since.

[Helmsman]

Originally Posted by Helmsman

Haha, always exciting to return to an old thread and find I thought I had it all figured out.

Well my turn - Replaced the battery. Once coding and register was confirmed (using Bimmergeek), I all of a sudden get increased charge voltage at 14.8V vs 14.3 isch with the worn out battery. Temperature has fallen to below 0 which apparently is being compensated by the ECU, but reading this thread an old battery apparently should be compensated with higher charge voltage puzzles me. I also went from AGM to flooded which again should lower the voltage if anything.
Yours has been fine since replacement or noticed any further odd behaviour Redd?

To conclude on this fwiw, turns out the battery mgmt system does more than I understood. This morning coming out from 20C garage the charge voltage on my new battery was 13.9V. On my way back home from office after a day in -5C, charge voltage was back up to 14.8V. So all seem good, temp compensated by the ECU more than I realized.

[Redd]

Originally Posted by Helmsman

Haha, always exciting to return to an old thread and find I thought I had it all figured out.

Well my turn - Replaced the battery. Once coding and register was confirmed (using Bimmergeek), I all of a sudden get increased charge voltage at 14.8V vs 14.3 isch with the worn out battery. Temperature has fallen to below 0 which apparently is being compensated by the ECU, but reading this thread an old battery apparently should be compensated with higher charge voltage puzzles me. I also went from AGM to flooded which again should lower the voltage if anything.
Yours has been fine since replacement or noticed any further odd behaviour Redd?

Mine has been fine aside from the initial period of low voltage. Consistent 13.8-13.9V while driving now. Like u said, I think the new battery registration does more than we realize.

[Helmsman]

Originally Posted by Redd

Mine has been fine aside from the initial period of low voltage. Consistent 13.8-13.9V while driving now. Like u said, I think the new battery registration does more than we realize.

Meeting again on good old subjects Eric....

Replaced my battery (to a 95Ah AGM from an 80Ah acid that went crap in less than 2y...).

Measuring with Carly (an area where Protool do nothing) turns out that the alternator turns down the voltage output and subsequently the current. Not below 12V as in your case but 12.1-12.3, assumingly where a new battery would be with some load without alternator support. It seems to vary the output so occassionaly well over 14V to suddently drop again.
Previous battery always run with a good 14-14.6V.

Found some BMW pwr mgmt stuff that state that the various consumers should use the alternator output as long as possible, to only when not enought start to consume from the battery. Seems the other way around in your and mine case...always something going on with these cars...

So how did it continue in your case, voltage gradually came up and all fine?

Did you test the alternator yourself or handed it in?

Thanks
Nik

Ps. Adding mentioned desciption.

[Helmsman]

Originally Posted by Helmsman

Meeting again on good old subjects Eric....

Replaced my battery (to a 95Ah AGM from an 80Ah acid that went crap in less than 2y...).

Measuring with Carly (an area where Protool do nothing) turns out that the alternator turns down the current output and subsequently the voltage. Not below 12V as in your case but 12.2-12.3, assumingly where a new battery would be with some load without alternator support. It seems to vary the output so occassionaly well over 14V to suddently drop again.
Previous battery always run with a good 14-14.6V.

Found some BMW pwr mgmt stuff that state that the various consumers should use the alternator output as long as possible, to only when not enought start to consume from the battery. Seems the other way around in your and mine case...always something going on with these cars...

So how did it continue in your case, voltage gradually came up and all fine?

Did you test the alternator yourself or handed it in?

Thanks
Nik

Ps. Adding mentioned desciption.

Thought worth an update for the next guy.

Here I am thinking I understand simple pwr mgmt systems...while as usual Redd is right.
Logging some more data (using Carly) it does seems like the battery is feeding everything till a certain point when the alternator is switched on. For instance turning on the fan (big consumer, like 30 amps) the alternator is switched on.

Never seen this with previous two battery replacement but seems to be the case. It is strange in my mind that the battery is allowed down to by Redd mentioned 70% or so before being supported by the alternator, as close to full maintain life time better. Also strange that the alternator seemingly haven't shut off after external/trickle charger been on. Learning stuff after 10y with this car!

Means that the BMW doc I posted above stating "The alternator is designed to supply current to all electrical loads and charge the battery.
If the alternator is not able to supply sufficient current to the electrical loads the additional current requirement is taken from the battery", doesn't seem to apply to our cars.

[Redd]

Thanks for reviving this old thread! I think it has helped me solve an issue I had with LiFePo4 batts.

Couple years back I tried using LiFePo4 batt. Registered it as a 72Ah AGM batt. The LiFePo4 batt worked fine for the first 200-300km, then strange things started to happen. For some reason, the alt would not charge the batt. It would let the batt run to 0% (even while I was driving the car), I'd have to jump start the car, then the alternator would charge the batt to 100%. After that full charge, it would let it run flat again. Rinse and repeat. During this time there was no increased battery discharge issues.

Alternator checked out ok. Removing and subsequently replacing the IBS battery cable did not solve the issue. In the end I went back to a normal AGM batt and everything was OK again. I never managed to get to the bottom of the issue, just chalked it up to incompatible battery (it was a China brand) and never used it again. Strangely, that same battery works fine in my Alfa 159 and other non-M3 BMWs.

This thread has reminded me again of the weird charging behaviour of our M3 alts. Maybe what was happening is that - for some reason - the DME keeps thinking the LiFePo4 batt is above 70% charge and does not activate the alt to charge the batt. Maybe cos the LiFePo4 current/voltage is high indicating strong charge or something.

With this new revelation I might try the LiFePo4 batt again but this time without registering the batt to see if it makes a difference.

[Helmsman]

Originally Posted by Redd

Thanks for reviving this old thread! I think it has helped me solve an issue I had with LiFePo4 batts.

Couple years back I tried using LiFePo4 batt. Registered it as a 72Ah AGM batt. The LiFePo4 batt worked fine for the first 200-300km, then strange things started to happen. For some reason, the alt would not charge the batt. It would let the batt run to 0% (even while I was driving the car), I'd have to jump start the car, then the alternator would charge the batt to 100%. After that full charge, it would let it run flat again. Rinse and repeat. During this time there was no increased battery discharge issues.

Alternator checked out ok. Removing and subsequently replacing the IBS battery cable did not solve the issue. In the end I went back to a normal AGM batt and everything was OK again. I never managed to get to the bottom of the issue, just chalked it up to incompatible battery (it was a China brand) and never used it again. Strangely, that same battery works fine in my Alfa 159 and other non-M3 BMWs.

This thread has reminded me again of the weird charging behaviour of our M3 alts. Maybe what was happening is that - for some reason - the DME keeps thinking the LiFePo4 batt is above 70% charge and does not activate the alt to charge the batt. Maybe cos the LiFePo4 current/voltage is high indicating strong charge or something.

With this new revelation I might try the LiFePo4 batt again but this time without registering the batt to see if it makes a difference.

I bet you're right (again) Eric. The Lithium batteries I had in my boat kept an impressive 13.2 volt basically regrdless of load and pretty much stable down to finished. Great characteristics in most applictions but maybe not in the M3. Clearly guys like Antigravity have solved this with their product.

I guess battery voltage and Ah capacity are used in some clever algorithm where the latter must be quite imprecise after some time.

Cheers

Edit: Found another piece on the alternator that says: "Higher capacity reserve as battery is never fully charged. A fully charged battery (100 % charged) cannot accept energy and is therefore avoided as part of the intelligent alternator control strategy."
Assumingly to leave space for the alternator to do its job when it's deemed most efficient. So starting to make sense; the alternator does provide all current needed and when not enough the battery takes on. BUT with the difference that the battery not is meant to be fully charged but should be kept at 70-80% capacity.
Redd, maybe one way to align the system to your Lithium is to change the voltage regulator in the alt. Takes a bit of research though...:-)

[Redd]

So after this thread revival I decided to give the LiFePo4 batt another try. Same brand of batt as before, but this time I used an 100Ah model which will hopefully be more compatible with our DME. Also, this time I did not register it as a new batt.

Lo and behold, the LiFePo4 batt works perfectly now! It's been 3 months and 2k kms on the new lithium batt and zero issues. I'm not sure whether it was the new 100Ah model or skipping the new batt registration step that solved the issue. Honestly I would just skip new batt registration going forward. Anecdotally, I've not heard of any real world difference in battery lifespan between those who perform the new batt registration and those who don't.

[Helmsman]

Originally Posted by Redd

So after this thread revival I decided to give the LiFePo4 batt another try. Same brand of batt as before, but this time I used an 100Ah model which will hopefully be more compatible with our DME. Also, this time I did not register it as a new batt.

Lo and behold, the LiFePo4 batt works perfectly now! It's been 3 months and 2k kms on the new lithium batt and zero issues. I'm not sure whether it was the new 100Ah model or skipping the new batt registration step that solved the issue. Honestly I would just skip new batt registration going forward. Anecdotally, I've not heard of any real world difference in battery lifespan between those who perform the new batt registration and those who don't.

Congrats mate, never giving up pays off...:-)

While skipping the registration, did you still changed the coding/capacity to the new battery Eric?

[Redd]

Originally Posted by Helmsman

Congrats mate, never giving up pays off...:-)

While skipping the registration, did you still changed the coding/capacity to the new battery Eric?

I had previously coded the batt to 92Ah non-AGM and this time I did not change the coding nor register it as a new batt.

[Helmsman]

Originally Posted by Redd

I had previously coded the batt to 92Ah non-AGM and this time I did not change the coding nor register it as a new batt.

Go it. And for the previous 72Ah Li, did you code for the low capacity? Trying to understand why the larget Li suddently works.

[Redd]

Originally Posted by Helmsman

Go it. And for the previous 72Ah Li, did you code for the low capacity? Trying to understand why the larget Li suddently works.

Yehw previous Li batt which did not work properly i did code for both capacity and new batt registration.

[Helmsman]

Originally Posted by Redd

Yehw previous Li batt which did not work properly i did code for both capacity and new batt registration.

Aha, was thinking the capacity was set too hight and fooling the system to not charge, but there went my last idea to why the current Li works and not the other...

[dnbtse]

Originally Posted by Redd

Yehw previous Li batt which did not work properly i did code for both capacity and new batt registration.

Hi,
I’m experiencing a strange voltage issue with my BMW E91 330D N75. Last month, I had a charging fault appear on iDrive. Mechanic diagnosed the issue as a faulty alternator, which was then replaced. However, after the replacement, I noticed a strange problem: the voltage would drop to 11.5 volts when the heating was on full blast in the morning but would slowly recover after turning the fans off. Sometimes it stay stuck the voltage stays at low voltage.
I then replaced the battery with one of the same specifications and registered it using Bimmerlink, but the problem persisted. The garage agreed to replace the alternator again after I demonstrated the voltage drop issue. With the new alternator, the initial fault was resolved, but I’ve encountered a new, problem.
For the past five days, I’ve been monitoring the car’s voltage during my daily work commute. Here’s what happens:
• Morning Journey:
When I start the car, with the windscreen heater and heated seats on, the voltage reads around 15.1V. After a 10-20 minute drive, it stabilises at 14.6-14.9V and usually sits around 14.8V. This seems normal, though 15.1V feels slightly high.
• Evening Journey (Issue):
When I start the car for the return trip, everything initially seems fine, with the voltage at 14.8V. However, as soon as I start driving, the voltage drops to 12-12.5V whenever I accelerate. When I coast or come to a standstill, the voltage rises back to around 14-14.5V.
If I turn the fan on full while driving, the voltage increases to around 13.5V. During steady motorway driving with cruise control and no traffic, the car seems to be running mostly on 12-12.5V, drawing directly from the battery rather than the alternator. Once I get home and restart the car, the voltage is back to normal at around 14.5V without any issues.
Could this be another faulty alternator, or is the car’s smart charging system causing this behavior since the new battery was registered? It’s strange that this only happens on the evening journey! Also last night I have another error message on the idrive Increased Battery Discharge, would this all be related ?

Scanned car, with Bimmerlink only error I can see is Glow Plug Module which I had replaced 4 years ago but the symptom was a rough idling so I don’t think it will be the Module causing all this specially in the evening only as the temputure is warmer the Glow Plug wouldn’t be cornering ?

But this morning i noticed it was doing the same thing as the evening drive so i think it is tempeture related as this morning was warmer weather. It started to rain today and i put the wipers on and the voltage shot up to 14volt solid, this makes me think its not the alternator as it is reacting to the needs.

i wonder is it the same as what you had at the start, have a done a bit of digging, it might be Brake Energy Regeneration disengaging the alternator because battery is near full?

P.s sorry to bring up such an old post again lol

[Redd]

The BMW power management system is pretty complex and does some weird things, especially right after new batt registration. Keep monitoring but give it a few months and see if voltage stabilizes after that. As long as it doesn't leave you stranded with a flat batt I wouldn't worry too much about it.

[Helmsman]

Originally Posted by dnbtse

Hi,
I’m experiencing a strange voltage issue with my BMW E91 330D N75. Last month, I had a charging fault appear on iDrive. Mechanic diagnosed the issue as a faulty alternator, which was then replaced. However, after the replacement, I noticed a strange problem: the voltage would drop to 11.5 volts when the heating was on full blast in the morning but would slowly recover after turning the fans off. Sometimes it stay stuck the voltage stays at low voltage.
I then replaced the battery with one of the same specifications and registered it using Bimmerlink, but the problem persisted. The garage agreed to replace the alternator again after I demonstrated the voltage drop issue. With the new alternator, the initial fault was resolved, but I’ve encountered a new, problem.
For the past five days, I’ve been monitoring the car’s voltage during my daily work commute. Here’s what happens:
• Morning Journey:
When I start the car, with the windscreen heater and heated seats on, the voltage reads around 15.1V. After a 10-20 minute drive, it stabilises at 14.6-14.9V and usually sits around 14.8V. This seems normal, though 15.1V feels slightly high.
• Evening Journey (Issue):
When I start the car for the return trip, everything initially seems fine, with the voltage at 14.8V. However, as soon as I start driving, the voltage drops to 12-12.5V whenever I accelerate. When I coast or come to a standstill, the voltage rises back to around 14-14.5V.
If I turn the fan on full while driving, the voltage increases to around 13.5V. During steady motorway driving with cruise control and no traffic, the car seems to be running mostly on 12-12.5V, drawing directly from the battery rather than the alternator. Once I get home and restart the car, the voltage is back to normal at around 14.5V without any issues.
Could this be another faulty alternator, or is the car’s smart charging system causing this behavior since the new battery was registered? It’s strange that this only happens on the evening journey! Also last night I have another error message on the idrive Increased Battery Discharge, would this all be related ?

Scanned car, with Bimmerlink only error I can see is Glow Plug Module which I had replaced 4 years ago but the symptom was a rough idling so I don’t think it will be the Module causing all this specially in the evening only as the temputure is warmer the Glow Plug wouldn’t be cornering ?

But this morning i noticed it was doing the same thing as the evening drive so i think it is tempeture related as this morning was warmer weather. It started to rain today and i put the wipers on and the voltage shot up to 14volt solid, this makes me think its not the alternator as it is reacting to the needs.

i wonder is it the same as what you had at the start, have a done a bit of digging, it might be Brake Energy Regeneration disengaging the alternator because battery is near full?

P.s sorry to bring up such an old post again lol

As Redd says, the system behave a bit weird/clever, from what I read things seems ok in your case with a new battery. As discussed earlier in the thread charging is disabled when battery is judged 75-80% full. At start it gets on it but again if ok filled up the voltage/charging is reduced.
Temperature is also a factor that makes a difference where I measured higher charge voltage when cold, as it should as the battery then needs it to accept charge.