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08-23-2019, 10:04 AM | #1 |
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Low voltage after new battery
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? |
08-23-2019, 11:21 AM | #3 |
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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.
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08-23-2019, 05:08 PM | #4 |
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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 |
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08-23-2019, 06:59 PM | #5 |
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A faulty EDC module will drain the battery continuously
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08-23-2019, 08:33 PM | #7 |
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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. |
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08-23-2019, 08:45 PM | #9 |
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08-24-2019, 03:42 AM | #10 | |
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Quote:
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08-24-2019, 03:43 AM | #11 |
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08-24-2019, 03:45 AM | #12 | |
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08-27-2019, 07:58 AM | #13 |
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09-13-2019, 07:01 PM | #15 |
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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. |
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09-14-2019, 02:46 AM | #16 | |
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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. |
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09-18-2019, 01:21 PM | #17 |
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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.
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09-18-2019, 07:07 PM | #18 |
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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? |
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09-18-2019, 07:15 PM | #19 |
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What are the symptoms/codes for a bad FRM? I have no errors right now and battery is charging according to my CTEK.
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09-18-2019, 07:17 PM | #20 |
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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.
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09-19-2019, 03:00 AM | #21 |
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Too low. This wouldn't be an FRM related issue. It would be alternator or IBS system.
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