[soulcrusher]

Good afternoon
I've been driving my E92 07 less frequently due to the pandemic and decided to maintain my battery with a trickle charger- output 12V 1.25A- in the past 2 days.

It required 5-6 hours until the trickle charger status changed from charging to storage. I charged from the hood terminals.
-------Background Context Over------

I took the battery to a auto-shop to test the cells. A diagnostic tool with clamps were placed on the HOOD terminals. Ignition off. Results read:
1- The battery is overheating, 102
2- Bad battery, Replace. 12.5+V at 89%

For a second opinion at another auto-shop. I redid the diagnostic at the hood terminals. Same results. Out of curiosity we tested the alternator.
1- Bad diode(s)

The alternator was bought recently, months ago. Currently its supplying 14.06V at the hood terminals, vs 13.99V at the battery terminals in the trunk. Specs 900CCA@0F RC185 AAA


a, Can I still run my vehicle with a new battery and the same alternator? The alternator is a time consuming part to replace.
b, And why is the battery overheating? Or, did the diagnostic tool mistook the temperature of the hood terminals? How does the tool measure temperature, by direct contact?

Any answers or insights are appreciated!! THANK YOU IN ADVANCE


[update] I removed the battery and had it tested independently. It tested well. I'm confused why the auto-shop tools detected a problem.

[Steve Sas]

Your meant to test battery when its disconnected from car. Not sure how they are measuring battery temp, maybe they are just trying to sell you a new battery.

Your alternator diodes may have a issue but you will usually not get 14v output??

What seem to be wrong with the car. Is the battery going flat overnight?

[e91Owner]

As the last poster said, you won't get an accurate reading from the terminals in the engine bay. Most of the testers I've seen won't even read anything and just show an error if you attempt to use them there. They should just be able to check it from the battery terminals in the trunk, though without removing it.

It's not very hard to check the alternator with a multimeter to make sure it's putting out around 14v yourself.

[soulcrusher]

Originally Posted by Steve Sas

Your meant to test battery when its disconnected from car. Not sure how they are measuring battery temp, maybe they are just trying to sell you a new battery.

Your alternator diodes may have a issue but you will usually not get 14v output??

What seem to be wrong with the car. Is the battery going flat overnight?

Thank you for the response! The car has showed no complaints. I decided to check up on the battery to verify its overall health. The alternator was tested out of auto-shop routine.

I'll re-check the voltage output of the alternator again this week. I expect it to be within healthy parameters.

One thing Ive neglected in my maintenance is not registering the battery. It's reserve capacity (185) is slightly higher than factory and calculates to 108Ah.
Currently my EMU is set to 90Ah. My options are between 90Ah and 110Ah in the EMU settings, correct?

[soulcrusher]

Originally Posted by e91Owner

As the last poster said, you won't get an accurate reading from the terminals in the engine bay. Most of the testers I've seen won't even read anything and just show an error if you attempt to use them there. They should just be able to check it from the battery terminals in the trunk, though without removing it.

It's not very hard to check the alternator with a multimeter to make sure it's putting out around 14v yourself.

Thank you for the clarification. One reason why it was not tested at the battery terminals is because the diagnostic tool the auto-shop used had large clamps, that could not bite down on the terminals.

Ill re-check the voltage output of the alternator again this week. I expect no changes or a voltage around 14.02.

I'm also thinking of registering my battery. It's RC (185) is slightly higher than factory. Calculated around 108Ah. My EMU is set to 90Ah. I recalled the only optional settings were 90Ah and 110Ah. I believe I've read that 110Ah should be fine?

[Steve Sas]

You can monitor battery voltage via kombi display. not exactly on the battery but close enough.
The voltage may vary because its set by the ECU as it controls alternator charging depending on systems demand.

[e91Owner]

Originally Posted by soulcrusher

I'm also thinking of registering my battery. It's RC (185) is slightly higher than factory. Calculated around 108Ah. My EMU is set to 90Ah. I recalled the only optional settings were 90Ah and 110Ah. I believe I've read that 110Ah should be fine?

Since it is super easy, I've only used Carly to register batteries which I'm sure results in preset values for a stock battery. Using ISTA-D or INPA may give you other options, but I'm away from my computer at the moment to look.