Low voltage after new battery

[Redd]

I recently had my battery replaced with a Banner 92Ah AGM battery. Banner are a BMW OEM supplier. Then I had the battery registered at a BMW specialist.

Here's the issue - Before I had my batt replaced, my voltage reading was a consistent 13.5 - 13.6V under all conditions. After the battery swap, it's been reading between 11.8V - 12.5V, even at higher rpms. Only occasionally it will go up to 13.5V. There are zero errors. I thought the new batt was poorly coded, so I had it registered a 2nd time, and also did an energy diagnosis for good measure. Alternator is working fine and charging the batt. I also have a CTEK Battery Sense and it shows that the batt is charging.

Are voltage in the 11.8V - 12.5V normal? Do new batts read less voltage? The alternator is only 37k kms old so I don't think it's due for replacement yet. Am I being overly worried?

[JP10]

Not normal during operation. Should be in the 14s. Seems like your alternator isn't quite getting you to where you want.

[Redd]

I know symptoms point to alternator. Just surprised why it would suddenly occur literally immediately after a new battery replacement. Maybe I will put my old batt back to test.

[ALCOBENDAS]

In acceleration its normal, disconect alternator to have more power.. retur to 13.6v when left the gas pedal..

With old battery detect bad status and not disconect alternator

Sorry my english

[///M Power-Belgium]

A faulty EDC module will drain the battery continuously

[Redd]

I don't have EDC. Plus the batt doesn't seem to be draining. Just the voltage is lower than usual.

[like2short]

It might be ok. Here's why:

The reason why you have to "register the battery" is because they charge the battery differently as it ages.

They do this to maximize fuel economy and to do this, they really just want to charge it when the car is coasting.

As the battery gets older, it needs to be charged differently.

Since your battery is new, it could be that they just decided not to charge it was much and hence the voltage is lower.

[Throatpunch]

Check engine ground
I just had this exact issue and replaced alternatorwhich didnt help

[ALCOBENDAS]

Thanks for nothing

https://www.google.es/url?sa=i&sourc...66697451797947

[Redd]

Originally Posted by ALCOBENDAS

Thanks for nothing

https://www.google.es/url?sa=i&sourc...66697451797947

I'm aware of Brake Energy Regeneration in our cars. I did check the voltage while braking but it did not change.

[Redd]

Originally Posted by Throatpunch

Check engine ground
I just had this exact issue and replaced alternatorwhich didnt help

The grounding strap near the exhaust pipe? I eyeballed that a few months ago and it was fine. But let me check it again. Thanks.

[Redd]

Originally Posted by like2short

It might be ok. Here's why:

The reason why you have to "register the battery" is because they charge the battery differently as it ages.

They do this to maximize fuel economy and to do this, they really just want to charge it when the car is coasting.

As the battery gets older, it needs to be charged differently.

Since your battery is new, it could be that they just decided not to charge it was much and hence the voltage is lower.

I really hope this is the case. I'll be taking the car to another specialist next week for some brake work and will get them to check the car again. Hopefully they don't find anything wrong either.

[Throatpunch]

Originally Posted by Redd

The grounding strap near the exhaust pipe? I eyeballed that a few months ago and it was fine. But let me check it again. Thanks.

no- the ground that is attached to the oil pan. it is not easy to see without removing the undertray

[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.

[Redd]

After 2 weeks of closely monitoring my voltage and battery charge level using the CTEK, I think this is normal after registering a new battery.

What I observe is that voltage will be low, 11.8-12.1V, when battery charge level is above 70-72%. Once it hits about 70% charge level, the ECU will tell the alternator to charge the battery. Voltage at this point goes up to 13.6V. When charge level reaches 85-90%, ECU will stop charging the batt and voltage will drop back down to 11.8-12.1V. Throughout this time, there has not been one single error. It seems to be normal operation.

Ground strap is in good condition. I even had the the battery registered a 3rd time at a second shop, and had them check the alternator also.

This seems to be inline with what like2short said above, and also what I've read in some other forums. When you register a new battery, it causes the ECU to change the charging profile of the batt. This is so as not to overcharge the new AGM battery, thereby prolonging its lifespan, and also to improve fuel efficiency. As the batt ages, it needs to be charged more frequently, so the ECU constantly charges it. This is what causes the constant 13.6V.

[Helmsman]

Originally Posted by Redd

After 2 weeks of closely monitoring my voltage and battery charge level using the CTEK, I think this is normal after registering a new battery.

What I observe is that voltage will be low, 11.8-12.1V, when battery charge level is above 70-72%. Once it hits about 70% charge level, the ECU will tell the alternator to charge the battery. Voltage at this point goes up to 13.6V. When charge level reaches 85-90%, ECU will stop charging the batt and voltage will drop back down to 11.8-12.1V. Throughout this time, there has not been one single error. It seems to be normal operation.

Ground strap is in good condition. I even had the the battery registered a 3rd time at a second shop, and had them check the alternator also.

This seems to be inline with what like2short said above, and also what I've read in some other forums. When you register a new battery, it causes the ECU to change the charging profile of the batt. This is so as not to overcharge the new AGM battery, thereby prolonging its lifespan, and also to improve fuel efficiency. As the batt ages, it needs to be charged more frequently, so the ECU constantly charges it. This is what causes the constant 13.6V.

Can't imagin its meant to go below 12v under any circumstances (when running). Never noticed this when I had my battery replaced and registered (by dealer). Should mean <12v when coming off the charger/being fully charged, which again is not the case for me. At this point it doesnt go full steam but still hovering around 14v maintenance charge.

After all all electronic systems onboard are designed for 14 (13.8v?) volt even if converting it down from there to the 5v and whatever needed.

[shuggy]

Have you gotten your FRM module replaced? BMW extended the warranty for that piece to 9 years / 125,000 miles or so. Faulty FRM drains battery and will eventually cause all sorts of startup issues.

[dpaul]

Helmsman is correct - voltage should never be below 12 (except during starting). This is not normal behavior for any type of battery.

How exactly are you measuring the voltage?

[Redd]

Originally Posted by shuggy

Have you gotten your FRM module replaced? BMW extended the warranty for that piece to 9 years / 125,000 miles or so. Faulty FRM drains battery and will eventually cause all sorts of startup issues.

What are the symptoms/codes for a bad FRM? I have no errors right now and battery is charging according to my CTEK.

[Redd]

Originally Posted by dpaul

Helmsman is correct - voltage should never be below 12 (except during starting). This is not normal behavior for any type of battery.

How exactly are you measuring the voltage?

I have a HUD device tapped into CANBUS (not using OBD port). Granted it reads about 0.5V lower than reading at the engine bay battery terminal when we checked at the terminal during troubleshooting.

[BPMSport]

Too low. This wouldn't be an FRM related issue. It would be alternator or IBS system.

[Redd]

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