Voltage/battery management issue

Blivit · Nov 10, 2024

I've been tracking down a voltage issue for a while now on my 2020. I have other posts here on it. Battery died suddenly and without warning in July of this year. No worries, replace the battery. After that it was fine for about 1 week then I was getting occasional slow crank. Never not starting but would often be very slow.
Yesterday the battery was dead, had to jump it. Got it going, drove for 30+minutes then turned it off. Try to restart and again, no start. Had to jump again. No error codes, no charging messages on the dash.

Connected battery to my charger over night and today I spent time checking voltage. Not running, voltage 12.5v. cranking it drops down to 9v. Running, it goes up to 13.6v and sometimes stays there. Other times it will go up to 13.6 then after running for a bit, drop down to 12.2. very inconsistent. Seemed alternator was not always charging or having issues doing so.

On a whim I disconnected the bms on the negative terminal. Voltage is now very consistent. When running it is always 13.5+. Not running still 12.5. cranking still drops down.

Could the bms be going out? With it disconnected there is a check charging system error but what other issues could this cause if I leave it disconnected for now?

I plan to take it in but no appointments available until 11/19 so seeing what I can do for now.

Blivit · Nov 10, 2024

Spoke too soon. It was starting (slowly) before I had to leave and had steady voltage. Connected the battery to my charger for 5 hours or so and came back to another no start. This battery is either toast after 3 months and/or there is a parasitic draw somewhere. I can't win.

Cdubya · Nov 11, 2024

The battery will be around 13.5V to 14.3V when alternator is charging. It will drop to near 12V when the battery is at state of charge 80%. 12.5V with the car off is respectable. Question is, what is the voltage after you leave it overnight? If the car is struggling to start, I bet that it is significantly low--parasitic draw. Also, did they reset the BMS when you swapped batteries? Since your battery is quite new still, i would dry that. You can do it with Forscan or look up the BMS reset procedure (it's been posted here in the forum somewhere).

Looking at your second post, are you saying it was on a battery charger and when you went to start it again, the battery was dead? That's a problem with the battery.

powerboatr · Nov 11, 2024

The battery state of charge setting from factory is 95%
That being said, even a short 20 minute commute will not bring battery to 95
Especially rear ac is on, and other highdraws
If you reset bms
And charged it to 95 or higher with charger
And then it drops to below 12 over night..agree woth above you have a huge parasite draw or bad battery
Do you have any added devices, that stay on
Like amps, or dash cameras
Did you disconnect battery and charge it, let it sit 12 hrs and check volts ?
In forscsn it's easy to data log charge system
Mine runs at 14.7 to 14.5. Afyer a start
Then in 5 or so minutes will level out at 14 ish
You csn also trick bms by ramping up blower for dash vents to 5 or 6 and withing a short time it will ramp up to 14
But your indications lean on bad battery
Or something huge staying live

Blivit · Nov 11, 2024

I have nothing connected to the vehicle (no lights, dashcam, no aftermarket stereo.)

I replaced the battery myself and did reset the bms when I did it.

After leaving it overnight, not on the charger, I don't see voltage below 12.

Last night it was connected to my charger. This morning, 12.4v at the battery, 12.2v read using my scanner at the obdii port. Tried to start, voltage on the scanner went down to 7.5v while cranking then back up to 12.2 after measured at the battery again at 12.4. Really hoping it's just the battery.

GomerPyleST · Nov 11, 2024

This might be a stupid thing to ask but did you replace it with another AGM battery and is it the correct size and cranking amps? Just asking because I have read elsewhere in other forums for other cars that some people when they replace the battery try and save money and replace it with a normal battery which will die sooner. Don't really think you did that but you keep mentioning 12.5V and AGM's are usually around the 14v area and just want to cover all the bases.

Blivit · Nov 11, 2024

GomerPyleST said:

This might be a stupid thing to ask but did you replace it with another AGM battery and is it the correct size and cranking amps? Just asking because I have read elsewhere in other forums for other cars that some people when they replace the battery try and save money and replace it with a normal battery which will die sooner. Don't really think you did that but you keep mentioning 12.5V and AGM's are usually around the 14v area and just want to cover all the bases.

Yes I replaced it with an AGM matching the factory specs.

GomerPyleST · Nov 11, 2024

Blivit said:

At this point I'd probably just take it to the dealer then and let them diagnose it (unless you know a better shop), however when I took my 2025 in due to my dash that keeps resetting every now and then (losing the pages I added to my view) they wanted to charge me $795 to diagnose it but only if they found mice damage. I told them you better not "Find" mice damage because my garage does not have mice and none of my other cars have ever had a problem nor does my wife's car which sits right next to mine. Also I only had it for like 2 weeks. Needless to say they did not find any mice damage (as I knew they would not because I also looked under the hood before I brought it in and it was pristine, no foam chewed up or any other signs) but they also said they could not duplicate my problem...so now every so often I have to re-add the pages to My View (Temp, Trip 2 and Drivers assistance) which is a bit annoying, but not too crazy of a gremlin and if that turns out to be my only gremlin then I guess I got lucky. Good luck to you though hope you find the problem.

Cdubya · Nov 11, 2024

powerboatr said:

Beg to differ. It's 80%. Easy to verify with Forscan. When set to 95%, voltage will be 14+V most of the time when running.

Blivit · Nov 11, 2024

Yay. I just took the battery to where I got it and it tested good there.

Starter, alternator, who knows but now it has to sit here until the 19th when I can get it to Ford.

powerboatr · Nov 11, 2024

Cdubya said:

Mine was at 95 brand new when I took delivery
That was 1st thing I went to change. So it would match my truck bms strategy
And it was already at 95...yes i thought at time..they must have updated the bms strategy already
7.5 volts starting is tooo low

Blivit · Nov 12, 2024

Quick follow up. Still will not start consistently. Cranks very slowly then eventually just stops most of the time. Seems like it is the battery but I have tested it using my battery tester as well as taken it to where I bought it 3 months ago. Both show good. My jump box will not get it started. Jump start will...sometimes.

Battery voltage readings:
1. 12.5v with the vehicle off
2. If I can get it started, voltage will go up to around 14v then settle back down to 12v or so.
3. During crank, voltage will drop down to 7v or so. This will happen even after charging the battery over night.
4. I let it sit overnight and not on the charger last night. Voltage was 12.4 yesterday then 12.3 this morning. Not what I would call a parasitic loss.

So I am stuck here. Everything I am able to check/do, I have done. Unfortunately I am not able to get it in to Ford until next week so we get to play the fun transportation game as my vehicles are manual transmission and my wife can't drive them

It really seems like it's the battery when it cranks....but the voltage is only dropping when cranking. Otherwise it charges normally and displays normal voltage. My thought now is that there is a ground issue or possibly a bad starter.

powerboatr · Nov 12, 2024

Out on a limb
Are cables to ground and at starter good, clean and tight
Something pulling a ton of Amps
I bet you all kinds of dtc s. At that voltage during start cycle

Blivit · Nov 12, 2024

powerboatr said:

Not easy to check those cables. No dtc codes now or ever during any of this.

powerboatr · Nov 12, 2024

Oh ue

Blivit said:

Yes starter is not user friendly
But something in start circuit is killing the battery, corroded connection, loose etc
The ford tech hopefully looks at that
You did say new battery was load tested correct?

Blivit · Nov 12, 2024

powerboatr said:

Yes it was load tested. I hope they can find something but I have to wait until next week.

Cdubya · Nov 12, 2024

Long shot but plenty of people have reported electrical issues shortly after a battery change--make sure all the terminals have been tightened down. They are all removed when taking out the battery.

Also, I do not think it's normal to drop to 7V when starting the car. I've had my car in ACC first and then started the car. If it was dropping to 7V, I'm pretty sure you would notice in the car, including my radar detector dropping out.

Cruising68 · Nov 12, 2024

Just did a couple tests with mine. Voltage is via Edge CTS connected to obdii port.

Battery 12.6 before test at the battery with meter.

Ignition on 12.0 dropped to 11.7 after 5 seconds.
Cranking to start 9.7-10v quick flash on gauge
After start 14.4

Repeated a few times with very similar results.

Sent from my iPad using Tapatalk

Blivit · Nov 12, 2024

Cdubya said:

At this point I've taken the battery out so many times I can do it in my sleep. I have definitely made sure everything there was tight.

Definitely not normal for the battery to drop that far down. Something is pulling it down when cranking. I do notice it obviously as it won't start. Right after trying to start, battery voltage is back to normal.

Blivit · Nov 12, 2024

Cruising68 said:

Mine is basically the same when I can get it started. If the cranking voltage drops below the 9v mark, it won't start.

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