40kWh Battery Charge indicator fluctuates wildly on acceleration

Hi all,

~1900 miles and having an issue where the battery level (%, and miles) can vary wildly during acceleration. During a recent trip it went from 43% to 3% in less than a mile of constant acceleration. Betty came on and reported low battery at 9% and quickly went to frantic "charge now" as readout dipped below 5 within a couple seconds. Nav display also switched to charger location map "to help". I own a 2016 30kWh, so I know how it should behave.

Eased off the pedal and charge level returned to 42%. This condition is easy to reproduce at any charge level below ~55%. The variance is not consistent, like 32 down to 12, or 40 down to 28, etc. I'm suspicious that the battery capacity sensor is defectively reading voltage fluctuation on rapid discharge as overall capacity loss, or the draw is interfering in some way. Dealer reproduced the erroneous readings, and ran the standard battery tests, but was unable to find a fault or determine a fix with NISSAN Corp technician.

I will bring it back after 2000 miles goes by. I am wondering if anyone else is seeing this or similar?

I didn't have leafspy running yet, but got it working again today and static driveway info on the battery looks fine, HX 110, SOH 98.25%, (404 GIDS at 81% SOC) , etc.

Since the miles to go GOM reading is generous, I do my own miles driven / % used to calc miles to go in my head as I drive, so the lack of consistent battery % level is challenging.

Sounds like a bad cell in your battery. Get LeafSpy and post a screenshot of the individual battery cells and we can confirm.

Have someone ride with you and take a video of it happening, then take it into the dealer. It should be fixed under warranty. However, if it doesn't throw codes, the dealer *might* give you a runaround. That's why having a video is key.

Where are you located--is it cold temperatures there? Have you checked and verified that the 12V aux battery is not old, weak or worn out?

i had similar symptoms occur in cold weather when a 17-month old Nissan aux battery that read 12.7 OCV was actually defective (probably over sulfated internally). The car was flat towed to the dealer and they didn't solve the problem either. i had suspected a bad cell in the pack, but they were all within 5 to 10 mV. A weak 12V can cause a multitude of issues across a wide variety of systems in an EV.

Good luck in troubleshooting.

I think that the bad cell(s) is more likely than a bad 1-2 year old auxiliary battery, but that can be checked as well.

You would think that the dealer could or would find a bad cell in a pack, but in my case they couldn't even troubleshoot properly to detect a bad 12V aux, so how much confidence can be given to ICE mechanics who don't drive or don't have road experience on how an EV normally functions? They are not software programmers nor electrical engineers, just good mechanics with tools that know how to follow instructions, change parts, and perform maintenance items.

Using a computer assisted tool to read DTCs is a good start, but what about a situation when no DTC points to the root cause? That's when EV experience, and an understanding of programming, CAN buss operation, electrical troubleshooting and tracing circuits, etc is needed, but that is not taught in auto shop class.

hoyaj said:

I own a 2016 30KW, so I know how it should behave.

Click to expand...

Battery capacity is measured in kWh, not "KW".

hoyaj said:

Eased off the pedal and charge level returned to 42%. This condition is easy to reproduce at any charge level below ~55%. The variance is not consistent, like 32 down to 12, or 40 down to 28, etc. I'm suspicious that the battery capacity sensor is defectively reading voltage fluctuation on rapid discharge as overall capacity loss, or the draw is interfering in some way. Dealer reproduced the erroneous readings, and ran the standard battery tests, but was unable to find a fault or determine a fix with NISSAN Corp technician.
...

I didn't have leafspy running yet, but got it working again today and static driveway info on the battery looks fine, HX 110, SOH 98.25%, (404 GIDS at 81% SOC) , etc.

Click to expand...

You should look at the max delta in mV between cells when you're at below 55% SoC, esp. when accelerating. Not sure what you mean by "battery capacity sensor". I don't think one exists.

I agree it sounds like bad cell(s)/module(s).

No bad cells reported in LSP; will have to look when battery capacity is lower, and running.

https://drive.google.com/file/d/0B4q-xJRiZuLOVkZ3b3FjempoX2VtVmhYOW82S0V1M3IxLTBV

https://drive.google.com/open?id=0B4q-xJRiZuLOWU1kek8wNzB5RHlBSzVhbHFMODJtY3lFWGVF

18mV spread min to max looks good based upon my experience with having a failed cell in an EV pack, and seeing the spread in other failed-cell packs.

My money is on a weak or worn out 12V starter battery.

hoyaj said:

No bad cells reported in LSP; will have to look when battery capacity is lower, and running.

https://drive.google.com/file/d/0B4q-xJRiZuLOVkZ3b3FjempoX2VtVmhYOW82S0V1M3IxLTBV

https://lh3.google.com/u/1/d/0B4q-xJRiZuLOWU1kek8wNzB5RHlBSzVhbHFMODJtY3lFWGVF=w640-h400-k-iv1

Click to expand...

You need to check it at lower state of charge, not capacity. Also, would be good to check under load (e.g. acceleration) while at that lower state of charge.

2nd link requires authentication, which I didn't want to allow. (If you want to test this, try opening a private/incognito browser window and try visiting it.)

Here's the output from LSP during acceleration:

https://drive.google.com/file/d/1uA-z1mWpM8nIeT15LnF6QCnAno2O5G82/view?usp=sharing

Looks like cell labeled 61 is not happy.

Good catch on the screen shot, a low cell like that would cause the charge indicator to fluctuate.

So it is either a weak or defective cell pair, or the measurement circuit is intermittent. Now it needs to happen such that it shows up when the dealer is testing.

Hope someone with an '18 or '19 service manual can comment on the voltages and criteria for its CVLI test. That way, OP can try to simulate that and then bring it to the dealer w/a similar state of charge and conditions (e.g. load on the battery, even better if the car's in park but with some load like the heater running at full).

But yeah, 200+ mV imbalance when under load at that high a SoC is NOT normal.

nlspace said:

Good catch on the screen shot, a low cell like that would cause the charge indicator to fluctuate.

So it is either a weak or defective cell pair, or the measurement circuit is intermittent. Now it needs to happen such that it shows up when the dealer is testing.

Click to expand...

Good news is that they replicated the problem already. :roll: Nissan tech support indicated that it would vanish as it learned how I drive.

I can't make this $%!t up.

^^^
What a bunch of BS. Have the dealer run thru the CVLI test procedure.

Oddly, the SoC meter has stopped fluctuating. I know the BMS is working overtime on this cell as I could see it rebalancing as I drove (large positive charge in that single cell when regen was active.