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For those wanting the graph, here it is. You can see the initial charge a few minutes after the logging started. The charging took about 18 minutes or so. Note there is a strange dip about a third of the way in - that's where my logging computer decided it needed to turn off. No idea why. Missed about 30 minutes of logging. But it should be pretty close.
Okay. 24-hour update. The 12V battery is fine. It is at about 12.64 volts this morning, which is basically still fully-charged. However, the HV battery is down to 78% again after 24 hours. The graph shows that absolutely no DC-DC charging is going on during the 24-hour period. Just the one charge cycle when I plugged it in, and then a very flat discharge curve for 24 hours. The 12V is never charged on its own, and at this point given the discharge curve, I'm confident that the 12V battery is not the issue at all now.
This brings me to an uncomfortable thought, which @ScottC2 has already raised, that it could be an issue internal to the HV battery. Specifically, a cell that is failing or not staying up to pack voltage, that the BMS is trying to balance over and over. In addition to the annoyance of losing a lot of charge, it raises significant safety concerns. There were two EQE fires, after all, and it's entirely possible this is a reason for it. Perhaps the affected cell(s) aren't really that below spec, but losing 1.5 kWh in a balancing attempt every day is far too much. I'm going to escalate this now with my dealership, and will bring them the information showing them that the 12V battery is totally fine and not part of the equation. Hopefully it's just something silly that's not shutting off and is currently sapping power from the HV battery, but I am very concerned it's loss due to balancing, which isn't a good place to be in. I'll update once I've had a chance to talk to the shop foreman, who is 100% on the ball here in Louisville.
Sorry to hear that , I hope its something silly too, otherwise it shouldnt be overlooked and quite serious as you said, only another low possibility idea left for me is the tyre pressure being affected by the cold weather , I read somewhere system shutdown some services if tyre pressure out of window range, maybe it triggers some software bug car thinks its idle long time but I can not think anything where would drain go then. Today I lowered my tyre pressure to 41-43 (it was only 3-4 psi higher after trip), reset the range(s) on driver display, disconnected ssd, shutdown mbux manually and will monitor again. I check there was no wifi or bluetooth signal from mbux after lockdown.
One question that does come to mind is whether or not we have active or passive BMS. In other words, can the BMS actually balance the cells without being under charge? It seems that with just open circuit voltage, it may be tricky to bring a cell up to charge using the rest of the pack, though I could be wrong on that. I do wonder if I should do a 100% charge for a while at some point to see if it'll top-balance, and then drive it down to sub-20. The problem is, the drain just keeps going, so something has to be going on that is active. I don't think it's just a calibration issue.
Unfortunate news, Bytemaster0!
I think performing the last experiment you suggested, if convenient, would be worthwhile doing before bringing the car to the dealer. It will give them fewer possible excuses to throw in your face to make you go away without doing anything.
It turns out the clicking doesn't stop even when the screens are off. This corresponds perfectly to an around 60W power drain. Something is causing the brake pedal to constantly reset itself every 23 seconds. I'm going to go back to the garage, but I'm almost certain this is it.
False alarm. The pedal stops clicking after another minute or two of the car being locked. Not the braking system. Also doesn't make sense to power brakes from the HV battery, as otherwise you'd have no brakes if the contactors opened. Back to square 0.
Last edited by bytemaster0; Mar 10, 2025 at 03:09 PM.
Okay, the thick plottens. I unlocked the car to pick up my kids. It showed 78%, the customary 2% daily drop. The drive to pick up the kiddos is 4 miles round trip, very short, but usually consumes 2-3% of power, especially if it's been colder outside. I came home, and parked. I just got back in to drive to my parents' home, and guess what? SOC still 78%. What?? Maybe it is a BMS calibration issue? Then what explains the 1kWh additions with the charge cable every day? I'm really confused now.
Unfortunate news, Bytemaster0!
I think performing the last experiment you suggested, if convenient, would be worthwhile doing before bringing the car to the dealer. It will give them fewer possible excuses to throw in your face to make you go away without doing anything.
Re-thinking my comment. If it is a failed HV cell, perhaps trying to charge to 100% would not be a wise thing to do right about now…
Re-thinking my comment. If it is a failed HV cell, perhaps trying to charge to 100% would not be a wise thing to do right about now…
Normally agree, though BMS won't try to charge a faulted cell. However, the SOC weirdness from today has me extra confused now. I drove without using energy, it seems! Loving my temporary infinity miles per kWh, lol. I think I'm going to charge to 100, drive it down to 80, then drive it under 20 and park. Maybe BMS will find its mind again.
I've top-charged the car to 100% and have driven for a while today. Went and picked up the kids and it barely took around 1% charge, so maybe my 78% double drive yesterday was just because the car is more efficient in this warm weather. Will keep driving the car and park below 20% to see if this is just a BMS glitch. Still waiting to hear back from the dealer.
Okay. Interesting update. I charged to 100% and then immediately left the house for some errands and to head to the lab. We took the car on a 90-mile trip as well. Did quite a bit of driving. (it's amazing how much driving you need to do to get the battery SoC lower). I parked the car last night at 51%, intending to drive further today and park below 20% to trigger BMS recalibration. And, what do you know, SoC was still 51% this morning! I'm still going to do the 20% recal, but this is encouraging. Maybe the 100% top balancing helped.
Okay. Interesting update. I charged to 100% and then immediately left the house for some errands and to head to the lab. We took the car on a 90-mile trip as well. Did quite a bit of driving. (it's amazing how much driving you need to do to get the battery SoC lower). I parked the car last night at 51%, intending to drive further today and park below 20% to trigger BMS recalibration. And, what do you know, SoC was still 51% this morning! I'm still going to do the 20% recal, but this is encouraging. Maybe the 100% top balancing helped.
Is it sort of like recalibrating a lithium ion battery on a battery powered device say a laptop or phone?
FWIW as a datapoint, I left my 2024 EQE (six months and 8K miles) unplugged for two weeks in February while out of town on vacation and there was negligible vampire drain. I don't recall exactly, but maybe 1%-2% at most. It was in an unheated garage with outside lows in the 30-40˚ range every night. I checked on it every couple of days with the app and saw no essentially no decline.
I was very surprised because my Model S's lost that much or more every day.
I think a healthy EQ has no detectable vampire drain.
FWIW as a datapoint, I left my 2024 EQE (six months and 8K miles) unplugged for two weeks in February while out of town on vacation and there was negligible vampire drain. I don't recall exactly, but maybe 1%-2% at most. It was in an unheated garage with outside lows in the 30-40˚ range every night. I checked on it every couple of days with the app and saw no essentially no decline.
I was very surprised because my Model S's lost that much or more every day.
I think a healthy EQ has no detectable vampire drain.
Awesome! Yeah, my dad's car lost only 2% after sitting for 2 months. I'm doing the overnight recalibration now at 17%. Tomorrow will charge back to 80 and see what happens the night after.
Plugged in the car this morning after over 12 hours. SoC was still 17%, so this is a second day of good news on the drain front. Hoping BMS recalibration is now complete. Charging to 80%, have a bit of driving to do today, then back to 80% tonight and see if it holds for tomorrow. Maybe the answer was to charge to 100% and let it top balance? Maybe combination new 12V battery and top balance? I'll post my (hopefully) final finding tomorrow once all of this process is complete.
Sorry bytemaster0 hijacking your thread too, reporting status: during prev. week I had around 1% daily drop, 1 day I get 0% but until I press start button then I got immediate 1% drop I dont know turning off mbux did a bit of saving or it was hot weather, I am suspecting same issue as you had because I get 3 times Power supply on error or trunk open error this week on different occasions even car was shutdown and fixed via shutting down mbux and re-locking car. I have found another user with your bus error code, he describes as ignition shutdown issue, I guess fixed via software update but please take my words with grain of salt. So I just returned from service now, they couldnt find anything with short 10 min diagnostic , mentioned also healthly 12V but they wanted to run full diagnostic and they will return car on Monday and they were willing to do further investigation that offer come from them, so I will update here if anything found.
Sorry bytemaster0 hijacking your thread too, reporting status: during prev. week I had around 1% daily drop, 1 day I get 0% but until I press start button then I got immediate 1% drop I dont know turning off mbux did a bit of saving or it was hot weather, I am suspecting same issue as you had because I get 3 times Power supply on error or trunk open error this week on different occasions even car was shutdown and fixed via shutting down mbux and re-locking car. I have found another user with your bus error code, he describes as ignition shutdown issue, I guess fixed via software update but please take my words with grain of salt. So I just returned from service now, they couldnt find anything with short 10 min diagnostic , mentioned also healthly 12V but they wanted to run full diagnostic and they will return car on Monday and they were willing to do further investigation that offer come from them, so I will update here if anything found.
Please hijack away! This thread is better with more reports.
The reason the battery percentage drops immediately after pushing the start button is because that's when the contactors close. Until then, MBUX has no idea what your state of charge is.
More updates from me: after the calibration run, the problem still remains at 80%. No "drain" at 51% or 17%, so this to me implies a weak cell that won't keep voltage. But after being parked 8-9 hours overnight at 80% SoC, it dropped to 79% as soon as the contactors closed. So, I'm going to pursue this vigorously with MB Service.
More updates from me: after the calibration run, the problem still remains at 80%. No "drain" at 51% or 17%, so this to me implies a weak cell that won't keep voltage. But after being parked 8-9 hours overnight at 80% SoC, it dropped to 79% as soon as the contactors closed. So, I'm going to pursue this vigorously with MB Service.
Sorry to hear about this! At least you have a long list of tests and verifications to give the dealer, which I hope would help them get to the root cause. Hopefully not a cell in the HV battery!
Sorry to hear about this! At least you have a long list of tests and verifications to give the dealer, which I hope would help them get to the root cause. Hopefully not a cell in the HV battery!
I'm about 90% sure it's a weak cell. It makes sense, because it only shows up at higher stares of charge. Or there's something going on that I really don't understand. I'm going to ask them to show me a breakdown of the cell voltages, and will bring it in at 90% or so. If there's an imbalance, we'll know.
Spoke to service adviser while we wait for MB central to get back to us. Next week, I'll charge the car up to 90% and let it sit for a while, then drive it over and they'll quickly plug it in and check individual cell voltages on SDS. They'll give me a printout to confirm. If I see a cell that's more than 0.05V different, we'll know it's a weak cell. At that point I'll see if they warrant that module
I charged the car to 70% last night. Turned it on, contactors closed, and after 22 hours or so, charge was 69%. One of two possibilities. 1. No matter what I charge it to, it'll always lose a little bit of pack voltage due to the (allegedly) weak cell. The reason it didn't drop when I parked at 51% and 17% is because the voltage drop had already occurred in the (allegedly) weak cell. 2. I haven't found the comfortable resting voltage of the (allegedly) weak cell.
Either way, will still move forward with the plan of bringing it in to check for voltage imbalance later in the day one day this week. Will post back after I find out more!
After parking overnight at 69% (1% drop since charge to 70 the day before), it was still at 69% when contactors closed 24 hours later this morning. That means to me that most of the voltage drop for the weak cell is at higher states of charge. The working voltage range of a lithium-ion cell is about 1.1V, and given the buffer in the car, I'd expect around 1.0V of working range. I charged the car to 80% this morning and will let it sit until tomorrow morning when I take it to MB to have them hook up SDS and get cell voltage reports. I expect to find one cell with a 0.02V imbalance, proportional to the pack capacity loss that I expect to have seen. I think the threshold for most of these cars on replacement of a battery module is 0.05V, or 5% voltage imbalance (which is rather high). So, what I'd have to do is charge the car to 90% while it's at MB, then unplug and leave it for a few days. I bet after 4 days I'd see a 0.08V imbalance, and they would then have to replace it. Of course, all of this is theoretical! Watch me get there and everything is perfectly balanced, who knows.
The sad part about all of this is that we shouldn't have to be engineers in order to be able to operate our EQ cars :-(
I guess it's just one of the many costs of being an early adopter.
The ongoing reports of this adventure has been riveting reading and quite fascinating. Thanks for making it public.
My conclusions having had nearly 2 years of ownership is this is a bit of chicken and egg situation. This requires lots of EV sales for dealerships to invest in training service technicians and then getting goods hands on experience from problems like this. Right now all the service departments have to contact Germany to escalate any unsolvable technical issues, and that must be a bottleneck leading to delays. This will get better, but it will take time. Yes, this is the price we pay for being early adopters.
Folks, I did some bad math in post 97, my apologies. I wasn't thinking about it thoroughly as a whole pack. Updated thoughts below.
EQE uses a 90s4p battery arrangement. 90 cells in series, 4 in parallel per series step. EQE has 10 total module packs, EQS has 12. Voltage range of a lithium ion battery is 4.2V (max) to say, 3.1V, maybe 3.0 (min). Assuming a top buffer of 2.5% (might be larger in reality), that means our operating voltage range is roughly 4.17V to 3.1V, (not 4.1 to 3.1 that I had said earlier) range.
90s means that pack voltage is at maximum (removing some for the top buffer of around 2.5%) 375V or so (4.17V * 90). At 80%, we are talking a nominal pack voltage of 300V or so.
Total cell count is 360 cells, likely pouch cells. 90.6kWh (usable) means roughly 250Wh per cell (again, usable, bulk is higher).
If I'm losing 2%, and we isolate it, as an exercise, to one or more of the individual 90s4p cell packs, that means that the expected voltage differential would actually be significant - much more than 0.02V that I described earlier. In each parallel 4p cell group, if only one drops voltage, they all drop voltage. So, dividing 300V at 80% by 90 cell groups means that a 2% loss in capacity (I'm directly translating to voltage and ignoring Ah capacity, as the BMS will do the same) means a voltage drop in total of 6V over the entire pack. That's pretty significant, and leads me to believe that I may have several weak cells, not just one. So, it's likely a group of cells that are imbalanced or low, and it should show up in a printed report pretty noticeably. At least, that's my theory. We'll see tomorrow afternoon!
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