Measurement point(s) for 12V?

[SalsabyJake]

Hi, I have a FixD OBD scanner dongle I bought years ago and when I run a scan on my '23 MachE Premium (Dec '22), it reports about 11.5V and "low".
I also measured the two 12V accessory outlets in the trunk/center console and (in accessory mode ON) they measured around 14.2V.
My understanding is that a fully charged healthy 12V MME battery is 12.85V nominally. So, I'm wondering if:
1. Is the OBD value is in error?
2. Are the 12V jacks converted from the HVB or are they direct from the 12V battery? (seems the former)
3. Are there any other convenient points to measure the 12V battery voltage with a voltmeter. (so one doesn't have to remove panels in Frunk!)

Thanks,
Jake

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[Teslaeata]

You will get voltages of 14 point something if the car’s awake because the DC/DC converter is charging the 12V battery and it’s the charging Voltage you’re measuring, not just battery Voltage.

 

[Teslaeata]

Apparently optimal resting voltage of charged AGM battery is typically between 12.7 and 12.8 volts. Not sure how you’d measure that unless you could creep up on the car without the key to avoid waking it up and drop Voltmeter onto the battery directly.

Unless car’s systems are telling me something’s up with the 12V battery I don’t tend to worry because the battery management system works just fine for me and won’t charge unless 40%, or even as low as 30% SoC.

 

[SalsabyJake]

You will get voltages of 14 point something if the car’s awake because the DC/DC converter is charging the 12V battery and it’s the charging Voltage you’re measuring, not just battery Voltage.

This is absolutely correct! I measured with the OBD scanner in accessory mode and it was 14.0V. Thanks for that clarification.

Now my only concern is that the battery is measuring in the "11s" when the car is off and door open. (I've seen 11.2 to 11.7). I've read so much about 12V battery issues, I was thinking of pro-actively replacing the 12V battery at around 2 years. But when I saw the 11.2V reading I was a bit freaked out.

 

[Snakebitten]

It's difficult to get static voltage readings on these modern vehicles because just approaching them wakes them up and you then get a false reading.

I installed a Bluetooth voltmeter on the AGM and I can get a reading without waking the vehicle.
Here is what I got just a few seconds before typing. I'm in the RV, the Mach-E is outside.

It also logs the voltage 24/7/365.

Here is today and you can clearly see my trips (circled) to the office this morning and the trip back home. (along with a couple of errands)

The voltmeter is about $25 and is perfect for these crazy vehicles.

 

[Teslaeata]

11.2V to 11.7V seems a bit low even for me who just don’t get excited about all the stuff written about others’ worries.

Attached chart shows a guide to battery charge percentages.

The Mach-e is supposed to start charging the 12V irrespective of whether turned on or off, plugged in charging or not so long as HV batt is over 15% SoC within 48hrs of 12V batt reaching 40% charge or immediately if 12V batt Voltage drops to 30%.

I’d have the 12V battery & charging system checked out by dealer unless you’re proficient at removing batt, charging and testing after full charge.

 

[Mach-e Husband]

It's difficult to get static voltage readings on these modern vehicles because just approaching them wakes them up and you then get a false reading.

I installed a Bluetooth voltmeter on the AGM and I can get a reading without waking the vehicle.
Here is what I got just a few seconds before typing. I'm in the RV, the Mach-E is outside.

It also logs the voltage 24/7/365.

Here is today and you can clearly see my trips (circled) to the office this morning and the trip back home. (along with a couple of errands)

The voltmeter is about $25 and is perfect for these crazy vehicles.

Care to share the identity of volt meter you purchased and how it is installed?

 

[phidauex]

Care to share the identity of volt meter you purchased and how it is installed?

I'm not the snake, but I believe it is this one: https://www.amazon.com/QUICKLYNKS-Battery-Monitor-Bluetooth-Device/dp/B01MT4583U/

Installation could land in a few places, but I'd be inclined to attach to the two jump points. Might be a more clever location elsewhere, maybe fusebox?

 

[Snakebitten]

Yes. That's pretty much the same one I have purchased. I have them on 3 vehicles.

I mount them directly to the AGM.

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