I'm glad we have you on here, Bytemaster0, because for me this makes my eyes glaze over.
Good luck at the dealer's tomorrow!

 

Okay. A few things to unpack. My dealer is awesome and gave me a full breakdown of all the cells. 90 cells in 2 packs, so 180 cells total (my estimate of 360 was based on a 90s4p configuration, but it may be a 90s2p - doesn't really matter for this discussion anyway).

The cell imbalance was much lower than expected. In pack 1, the imbalance from average (not maximum spread) was only 7 millivolts (0.007V), which is excellent. Max Pack 1 imbalance is 11mV, still excellent. Pack 2 has an imbalance from average cell voltage of 18 millivolts (0.018V), which is more than twice as much. However, even that is still overall pretty good. I don't see how I could be getting such a large predicted voltage difference (3-6V). That's just not happening according to these figures. The max spread of Pack 2 is 20mV - not super perfect, but still very good overall for an EV pack with that many cells.

So, I'm a bit unsure where to go from here. I will say that when the contactors closed today, my pack had dropped 1% instead of the customary 2% in 30 hours. Different for sure. And it hung on 79% for a while, indicating it wasn't about to drop to 78% as expected. And for those wondering, it was actually much colder last night than on previous nights, so it wasn't a low temperature vs. high temperature issue. I've attached the full diagnostic sheet (5 pages) from my battery in case anyone wants to take a look.

FWIW, MB will warrant a pack if voltage spread is worse than 70mV. A bit high in my opinion, but that's what they've said. That's max to min spread anyway, which is worse than min to average, so I guess that's fine. If anyone has further insights, especially if you have plenty of background on EV battery imbalance, let me know what you think! For now, I guess I'll ignore the issue, charge to 100% a few times to help the pack top balance some more (I basically never do), and then ask for another printout in a year or so to see where things are, and keep an eye out on capacity drops overnight. Per MB techs, my battery is very healthy, and for the most part, I agree. Let me know your thoughts!

 

Happy to hear that your dealer addressed issue in this way, also for your battery health bytemaster0! Also thanks for battery breakdown, I couldnt find anywhere else battery spec, definitely I have learned a lot from this thread. Myn postponed tomorrow morning I will go there. Definitely I am not in the experienced group, I just involved with EVs only one month, but I will just throw it here, no shame to ask your post #100 made me wonder in what cases bms kick in, that I wanted to see also what components involved, I found this link, would item #7 make any sense with your error code that it says bms needs constant power? But I dont know if your error was repeating or this is the standard bms spec.

 

Excellent research, but no obvious results.

At some point, when it is convenient, suggest you leave the car unplugged for a couple of weeks at about 50% SOC. Confirm that the 12V battery shows "Good, charged". Then check the SOC after 7 days and 14 days. Even better if you could leave it unused for 3 weeks.

The SOC loss should be no more than 2-3% over this time. Anything more than that will provide more statistical information.

 

So i just returned from service i have been told i got software updates also 12V battery replaced under warranty, but i didnt get any service paper about what they did or what was error, when i have asked errors today it was already reset so i dont know the codes but they said 12V was draining battery, They told me to return back if issue occurs again but they said then they will keep car longer.

 

Glad to hear they replaced the 12V. Good luck, hope your problem is resolved!

 

Thank you , lets hope so, I will go through this thread again and try to replicate how you guys did proper charging&monitoring or maybe lastone suggestion.

 

lol I lost 2% overnight

 

Ask them for the same printout I got. I'd be curious what your max cell spread is. If it's better than mine, maybe we have something keeping our BMS up at night. Too much coffee the day before?

 

Another wild idea. Check if there are any OTA updates "pending" that keep failing and re-trying?

 

I thought of this as well, but we'd notice on the 12V. My dealer also checked for any pending. I do suspect there is one pending soon, as EQB got BMS updates a bit ago

 

OK will do thx, that would be maybe good reference ,if its bms and looking at the components involved I dont see any reason that wake-ups can not be logged or monitored, I will ask them bms too

 

Ok going service now , I will also ask current errors after reset, same service battery report bm0 get,ota updates and bms issue

 

I think a common thread here is that if you drive the car after charging it, and then park without charging it, the pack won't drop. I think it's an issue of cell voltage dropping after charge, if I had to guess. Even though my pack looks pretty healthy. You can try driving it and the park overnight without charging. See if it drops any more. I bet it doesn't. Let me know what your dealer says.

 

I always do street parking overnight without charge and I do 22Kw mostly but once or twice a month I do dc charging from mids to 80% all of them done during the day, my eco mode on so even 175Kwh DC drops to max 67Kwh. More for ref: I got heat pump, year is 2024/2 , beside of overnight drops range is good.

Ok thanks to dealer I had access to detailed Xentry short test results (they got report as OTA , remotely btw), I didnt have error since yesterday, details were knowledge wise satisfactory but there wasnt anything suspicious about extra ordinary drain for my uneducated eyes. Report break downs each component and lists errors under this component with a classification letter : ✓, i, f, F . Letter breakdowns here. BMS was ✓ (vendor is hella), I didnt check codes yet but most of them looks like momentary loss of packet/comm. between components, its in Czech I will google them now.

My past errors since prod.:
Multifunction Camera - i - U016887
PTCU powertrain - f - U112A87
Driver Assist. Sys. - i - U186B29
DCCU - i - P13CD8F
Insturment Cluster - i - U011587
MBUX - f - B227D00, B1E7B00, B162997

HV Battery health/breakdown:
I showed bytemaster0 report, they recognised what it is, diagnostic guy was busy, we will schedule next visit for report with them in a week or two that will also give me time to see if there is any calibration going on.

They confirmed no pending OTA update, my last OTA was on MB me: 1/30/2025 upgrade comm module. I dont/didnt have any recall according to VIN.

End of report

 

@eqe300CZ , thanks for the detailed report! I'm curious to see what your dealer will show for the full battery report.

I do have one more update for the thread. I charged the car up to 86% while I was at the lab yesterday and drove home. SoC was exactly 80% when I pulled in to the driveway yesterday around 2:30 PM. I left the garage this morning after a few seminars, at around 10:30AM. SoC was still exactly 80%. And I continued to drive at 80% for a while, indicating there was no further drop.

My conclusion at this point is that the "drop" is not a drain. It's a voltage sag post-charging. At no point after driving have I seen the SoC drop further. It's only after charging and leaving the car there for a while. I cannot currently explain why after a snow storm the car was down to 72%. Maybe it was the 12V battery before it was replaced. But, for now, it seems that 1-2% voltage sag is evident after charging.

After I did the BMS recalibration, I will say that it appears to sag more slowly. As mentioned before, I'm going to do some 100% charges, at least a couple, to let it top balance. I may even try the sub-20% BMS recalibration a couple more times just for reference. If I see any new behaviors, I'll definitely post. For now, I know that: 1) There are no shorts in the pack, so I have no safety concerns at the moment. 2) Pack health is generally very good. 3) I'll just have to get used to that small amount of pack voltage sag after charging, until something else changes. For now, it's a small amount, and will easily go unnoticed. It was definitely a new behavior after nearly 2 years of ownership, but it sounds like I won't need to worry about it, and that the battery will likely long outlast the car chassis anyway. Thanks to all those who have followed and participated in this thread! I'll post more information if I find any!

 

Sure, I will share here I am also curious, yesterday I got again 2% but weather get cold again here -4&5C ish at night 15C during day at those drops, I didnt do BMS cal. yet.

2:30pm -> 10:30Am 0% , thats good news! I read also from other users that they got improvement of range after 12V change. Also your cell values were far from threshold, I will be glad to have those values!

 

OK I did BMS cal. charged to 100% yesterday then drove until 85% with small breaks each @ 2-3% that took me a while to drop. Today it was still 85% after 14 hours, at 15/6C temps. Its been around a week since new 12V. and a month since I did 100%

 

Great! Did you let it sit overnight under 20%? That does the low pack voltage BMS calibration. Charging to 100% top balances the pack somewhat.

 

Aha no sorry wrong info then, tomorrow going for trip, on my return I will charge it in a way to catch 20% range

 

Very good. It has to be below 20, so say, 18% is a good target.

 

And it has to be at that overnight (or equivalent period)

 

thx will do

 

Woah my battery was 78% yesterday I drove my way back around ~300 km on highways with 130km/h but I enter few cities as well as there were stops due to accident or some trucks, when I start estimated arrival was 13% but after arrival home using stops with regen soc was 17%, I left car overnight and morning was 12%, temp was pretty cold as well, I am wondering could regen compansate only buffer zone and the buffer area easy to go if car is not in optimal conditions due to temp? I also wonder if battery heating kick in overnight. But I read bytemaster0 doesnt use regen also he didnt have this before.Anyways tomorrow morning I will be at service they gave me available slot prev. week. If they say everything ok I will ask why , even they dont have answer I will ask them to reach MB tech if possible even if it takes time.

 

I do use regen, just not automatic regen. When I push the brake pedal, it regenerates, more so than if you use the other modes, it seems. The estimated percentage of arrival always goes up for me as I drive. It gives you a worst case estimate generally speaking. I always end up at a higher SoC with my trips.

One more caveat to the overnight BMS calibration - it needs to be over 10C°. The car generally won't heat the battery unless it's very, very very cold or you are preconditioning. No chance you had morning preconditioning enabled? Please let us know what you find!