Time to change my 12V battery (FFE 2018) ?

[TheThing2018]

Hello and thank you for your reply.

I purchased a brand new FFE in 2018 and my dealer suggest me to replace my 12V battery.
Odometer : 95000 kms (59000 miles), about 18000 kms/year
EV battery (the whole pack) was replaced under warranty 1 year ago (P0A95 / P0AA1 / P0AA0). The 12V battery was not replaced.

Forscan parameters :

V_Batt : 14.7 V
BATMOD : 14.2 V
BAT_CHA_DISPL : 90.5 %
BAT_PACK_VOLT : 343.04 V
BATTERY_AGE : 2316 days
BATT_INT_OC : OK
BAT_ST_CHRG : 93.0 %
BAT_V_DSD : 10.6 V
V_BATT_BCM : 14.55 V

About my EV cells :
Lowest cell : 3.982 V
Highest cell : 3.997 V
Average : 3.991 V

Most of the cells are above 3.992 V (with a small block of 6 cells block around 3.985 V)

May I have your opinion on this ?
Note : I live in Montreal, Qc, Canada and the weather in winter can be very low (-18C, 0 F). I drive about 60 kms/day, mostly in the city.

About the battery itself, I found that a 26R could be the right one.

 

[Anti_Climax]

The 12V battery and the HV battery are entirely separate, the health of one doesn't tie to the other aside from each needing to work.

Did they say anything about WHY they suggested it get replaced? Which module is reporting Battery_age?

 

[TheThing2018]

I know that these parameters are separate but, as a new user here, I wanted to display the actual health of my car.

As for your question, the dealer told me that they advise drivers to change the 12V battery to avoid problems in the future (whatever its condition. In fact, they didn't do a test, they gave their opinion when I went there to buy winter rims).
As far as they're concerned, the average lifespan of a 12V battery is around 5 years, and I'm a year over that.
What's more, winter conditions in Quebec are “notoriously” harsh, and a faulty 12V battery can cause the whole car to malfunction.

That said, I could do a boost if the 12V battery fails.
But I'll read your opinion with interest.
I can do a Forscan of other parameters, if necessary.

Thanks

 

[Anti_Climax]

Sounds like a judgement call. It looking good right now doesn't mean it won't have issues in the near future, so it's mostly a matter of how much trouble you can tolerate from a failure.

 

[hoprocket]

I would do it, and I plan to do it every 3 years or so going forward. I have suspicion, but no proof, that a low 12V battery was root or contributing cause of the HV battery death in my 2018 FFE.

 

[Anti_Climax]

What mechanism would you suspect for the 12V battery to damage the HV battery?

 

[hoprocket]

This is the code that started the high voltage battery death of my 2018 FFE:

Code: U0100 - Lost Communication With ECM/PCM A

Additional Fault Symptom ( :01):
- General Electrical Failure

I walked into my garage one evening and the high voltage contactors were clicking on and off, on and off, over and over again. The car was plugged into the 120V HV battery charger at the time. I pulled the above code right after that. I now suspect that a low 12V battery caused one or more of the modules to shut down/freeze/or just not operate properly while charging which possibly over-charged and damaged the HV battery due to the contactor cycling. I don't think the 12V battery itself was the problem, but rather a low state of 12V battery charge due to lack of driving during an extended "work from home" peroid. Again, I have no proof, but couldn't think of any other reasonable explanation. I could be totally wrong. Bottom line is I now think that assuring the 12V battery is in good shape and stays well charged is very important.

 

[Anti_Climax]

Overcharging is a practical impossibly. The contactors cycling over and over could certainly wear them out but they are external to the battery. Certainly if the 12V system dips low enough modules may drop off but the actual charging is handled by the SOBDM and if that drops due to low voltage it would not be generating output that would charge the HV battery.

 

[hoprocket]

What does the BECM module do? That's the one that lost communication with the ECM/PCM. I just assumed it was controlling HV charging. Even if it wasn't, I can say for certain the HV battery was never the same after that contactor cycling episode. Coincidence? Maybe.

 

[Anti_Climax]

BECM is the HV battery management system. It monitors individual cells, it's mostly the feedback for the SOBDM. If it stops talking the SOBDM would stop charging.

Could be the opposite - like it lost communication because it began to fall. I'm which case, yeah, it would be coincidental.

If communication is lost modules don't go wild. Not saying it's impossible but without some explicit confirmation of how it could have occurred, I can't see them being related.

 

[triangles]

in 8 years of ownership my FFE went through 3 12v batteries. Granted the first one was caused by the telematics module misbehaving and draining the 12V battery flat repeatedly over the 5 months it took the dealer to finally properly diagnose. After 2 lead acid batteries I went with a LiFePO4 12V battery. I'm in northern Ohio and it rarely gets below about 15F, -9C. I only had it for 1.5 winters though and didn't have any problems even though you're not supposed to charge LiFePO4 below 0C.

 

[Heima]

I am kinda with Hoprocket. After I had the 12V battery disconnected for 3 weeks. When I hooked it back up (it was fully charged and functional), things went crazy in the car. HV battery SOC went from 50% to 0%. After repeated module resets and SOC adjustments, the SOC returned to 38%. Not the full 50%. Since then, the HV battery behavior has been different. For example, If charging up to 100%, the car will eventually stop charging, but the pumps will continue to run, even though the temperature is fine and cooling unnecessary. Additionally, the BMS will not exit balancing, worse the cells aren't balanced. And balancing is done with the L1 charger now.

 

[Anti_Climax]

Guessing that was out of warranty so no dealership diagnostics involved (not that there's anything in the service manual for that)

 

[TheThing2018]

Thank you for all your comments. All very informative. I'm going to buy a new 12V battery and do the swap (and keep the old one, just in case...). Unless I'm mistaken, I should do a BMS reset when the battery is changed.

After this change, I'll leave another message here with the success (or not) of this change.