[unrulyteach]

I notice the other day when monitoring my car that while it was running i was only at 13.3v. Battery is new, had the battery tested multiple times from the jump post under the hood and it failed. Had the battery tested from the terminals in the truck while connected and what do you know the battery passed. Alternator is fairly new 2-3 years oem from bmw. There are no codes at all and i don’t notice any difference when radio, a/c, and lights are on.

[e91Owner]

Where you monitoring it from the hidden menu or from the engine bay?

If you were measuring it from the bay, I would do it in two locations:

From the jumping terminals and from the positive jump terminal to the block. If there is a significant difference between the two? I would suspect that you have a ground strap problem and should check the condition/replace as required.

If the voltage was fluctuating substantially with the car running on the hidden menu, I would suspect a bad voltage regulator.

[unrulyteach]

Originally Posted by e91Owner

Where you monitoring it from the hidden menu or from the engine bay?

If you were measuring it from the bay, I would do it in two locations:

From the jumping terminals and from the positive jump terminal to the block. If there is a significant difference between the two? I would suspect that you have a ground strap problem and should check the condition/replace as required.

If the voltage was fluctuating substantially with the car running on the hidden menu, I would suspect a bad voltage regulator.

I monitored voltage from obd2 using MHD

[kkasson]

Normal. If the battery is healthy and you don't have a lot of electrical load then it will lower the charging voltage to maintain the battery's health.

[e91Owner]

Originally Posted by kkasson

Normal. If the battery is healthy and you don't have a lot of electrical load then it will lower the charging voltage to maintain the battery's health.

13.3 is outside of the normal range of the voltage regulator, at least on an N52. That being said, until there’s an actual problem, I wouldn’t get too worried about it. Maybe someone else can post the correct range on the N55. Without looking it up, I don’t know if it’s the same alternator.

[marvinstockman]

Before you drive yourself insane, check your meter against another meter.

And, as was said, if you have no problems, you really have no problems.

[unrulyteach]

I will check a report back

[unrulyteach]

Measure with voltage meter and at both thr jump post and battery, results are thr same 13.3-13.5v

[marvinstockman]

Did you check with another meter?

I use this if I'm having issues: https://www.amazon.com/dp/B0BWF7LFGZ...fed_asin_title

[unrulyteach]

Interesting I’ll try that but with load on thr battery it does drop to around 13v but no signs of dying really odd

[unrulyteach]

So, i tested the alternator output from the positive post on the alternator and grounding it n the body and it’s right at 14v

[kkasson]

So you're getting 14v at the alternator but only 13v at the battery? In that case yes there's a problem. You'll want to check the voltage at different places along the path. IIRC the battery cable comes from the alternator and starter, goes across the engine bay and connects near the positive jump post on the other side the engine bay. Test the voltage there - if you're still getting 14v then that cable is okay, if you're getting 13v at the jump post then you're losing voltage across that cable.

Try both the jump post and where the cable directly connects underneath it.

If everything is good there, check the battery again. Test the cable coming into the battery, and the battery post itself to see if there's a bad connection between the cable and the post.

There was a recall years ago for problems with the positive battery cable between the front and back of the car.

Also double check to make sure that there's no voltage between the engine and the body. If everything else checks out then you'll need to figure out where you're losing voltage between the jump post and the back of the car, which is more difficult to do because the cables are all hidden inside.

[unrulyteach]

Originally Posted by kkasson

So you're getting 14v at the alternator but only 13v at the battery? In that case yes there's a problem. You'll want to check the voltage at different places along the path. IIRC the battery cable comes from the alternator and starter, goes across the engine bay and connects near the positive jump post on the other side the engine bay. Test the voltage there - if you're still getting 14v then that cable is okay, if you're getting 13v at the jump post then you're losing voltage across that cable.

Try both the jump post and where the cable directly connects underneath it.

If everything is good there, check the battery again. Test the cable coming into the battery, and the battery post itself to see if there's a bad connection between the cable and the post.

There was a recall years ago for problems with the positive battery cable between the front and back of the car.

Also double check to make sure that there's no voltage between the engine and the body. If everything else checks out then you'll need to figure out where you're losing voltage between the jump post and the back of the car, which is more difficult to do because the cables are all hidden inside.

Will test this tomorrow but i am getting 13.3v at the jump post

[ctuna]

If you have a rusted Ground Cable from the Engine to the Chassis
you could be loosing voltage there . This happens in area's that have salted roads or high humidity . The Ground Cable is under the starter motor.

https://www.e90post.com/forums/showthread.php?t=1839045

[unrulyteach]

an update 14v at alternator and 13.3v at the jump post. Took off jump post cover and tested the cable running across the engine where I'm guessing it comes from the the starter? Still 13.4v tested the cable that goes from the jump post to the white box still 13.4v I'll do a warm test later but I'm guessing my issue lies between the cable that runs across the engine and the alternator

[unrulyteach]

Testing voltage drop while car is running from alternator but to cable end that runs across the engine and the result was .71v