Bad Cell Module and balancing issues when braking

I have a 2013 with 2100 miles that already has a bad cell pair according to the equation provided by Tick Tock in the thread
http://www.mynissanleaf.com/viewtopic.php?f=30&t=11399&start=10

I have seen many posts about high cell variations, but I don't think I've seen any that have this high of a variation or where it is just ONE cell pair that is extraordinarily low.

Here are several pictures of the battery pack draining down on a day that I decided to turtle the car. the last 6% SOC was used by the heater while parked safely in my garage. This also means that from 15.8% down to 9% SOC the battery was drained very steadily and at the low rate of about 3 kW.

This screenshot is early in the discharge when cell #25 easily meets the criteria of being a faulty cell.



The cell variation gets progressively worse, and this screenshot was taken when I finally hit turtle. I had to use the histogram view because the other view was goofy.


The next day and most of the day after that, my entire pack was being shunted. That did seem to help, but cell pair #25 was still often low and definitely so under 40% SOC or so.

This cell pair #25 is nearly always the lowest cell voltage in my pack. I looked at all the data that my Leaf Spy has logged, and #25 is the lowest or next lowest over 50% of the time. The only times when it is not lowest or nearly the lowest is when I have a huge balancing issue due to braking or quick starts as shown in this screen shot just after coming to a stop at a light


Of course I've taken the car in (before I had the Leaf Spy data) and they said nothing was wrong. I even took it in at VLBW and insisted they test the battery. I don't really know exactly what they did test or measure because when I talked to the tech afterwards, I was sure he didn't understand what he was doing. I'm also pretty sure they fully charged it before even hooking up the OBD.

A couple other questions I have for you experts on the forum are:
1) What will be the outward effects of a bad cell pair and can a bad cell pair adversely affect the rest of the pack.
2) Is the 3rd screenshot (8:19PM) typical of when the car is being braked or is this evidence of another problem?

you should to some QC,and then check the battery.i am wondering about the Hx 113,91

I'd like to do that, but there isn't a QC anywhere that I can drive to. I got the car with a dealer swap and that 1 QC was already done before they swapped it. So you (xado1) think the Hx is too high? I thought that the Hx numbers were all bogus anyway.

not to high,but unusual for a new battery.how can i upload pics here?
here is a link,where u can see my battery.

http://www.goingelectric.de/forum/nissan-leaf/wieviel-gids-hat-euer-leaf-t2232-130.html#p62867" onclick="window.open(this.href);return false;

GroundHog said:

I have a 2013 with 2100 miles that already has a bad cell pair according to the equation provided by Tick Tock in the thread
http://www.mynissanleaf.com/viewtopic.php?f=30&t=11399&start=10

I have seen many posts about high cell variations, but I don't think I've seen any that have this high of a variation or where it is just ONE cell pair that is extraordinarily low.

Of course I've taken the car in (before I had the Leaf Spy data) and they said nothing was wrong. I even took it in at VLBW and insisted they test the battery. I don't really know exactly what they did test or measure because when I talked to the tech afterwards, I was sure he didn't understand what he was doing. I'm also pretty sure they fully charged it before even hooking up the OBD.

Click to expand...

Yeah, it looks like you might have a bad cell-pair. They need to run the CVLI test (what does that stand for, btw?) - if they didn't do this properly, then you need to try to convince them to do it. It can be difficult, as dealers often think they know more than owners do! It took quite a bit of convincing on my part to have the CarWings update applied to my car, for example.

Applying the formula that TickTock posted:

Cell voltage loss judgment value = Average cell voltage - (maximum cell voltage - average cell voltage) x 1.5
where Average cell voltage = total battery voltage ÷ 96

At your 33.7% screenshot:
3.777 - (3.787 - 3.777) * 1.5 = 3.762 (you had min 3.755 which is well under)

At your 9.0% screenshot:
3.181 - (3.233 - 3.181) * 1.5 = 3.103 (you had min 2.740 which is well under)

GroundHog said:

1) What will be the outward effects of a bad cell pair and can a bad cell pair adversely affect the rest of the pack.

Click to expand...

No ill effects, just a reduction in usable capacity.

GroundHog said:

2) Is the 3rd screenshot (8:19PM) typical of when the car is being braked or is this evidence of another problem?

Click to expand...

That is typical, the refresh rate of LEAF Spy is too slow to get even readings unless you have a very steady load.

What do the cell-pair voltages look like when the pack is 80% and 100% charged?

CVLI stands for "Cell Voltage Loss Inspection" from the EVB section of the service manual.
For speaking points to service, the manual does say "although not judged as malfunction in DTC",
so a DTC does need to be recorded. The manual also says the inspection is done when the minimum
cell voltage is 3.712 volts or less. I would think using the next to minimum voltage would make more
sense, since the minimum is the bad one, but they may want to use minimum as that is what is displayed.
Any way according to the manual this test is supposed to be done on a greatly discharged battery, they
suggest the 3.712 volts would be near 2 charge segments showing.
So the 1 image I think clearly shows a cell out of spec.
I have read somewhere on the forum that Nissan corporate has called an owner to tell them a
battery needed work after the annual inspection was done. Apparently battery data is sent to corporate.

drees said:

What do the cell-pair voltages look like when the pack is 80% and 100% charged?

Click to expand...

I finally got around to posting this. At 100%, the bad cell is still obvious and would meet the formula criteria. But from what Cliff posted, the minimum cell voltage is too high for the test to be valid and of course the variation is only a small 27 mV.

I will say that I started looking hard at my battery when I thought that I had a reduced range/battery capacity of about 10-15%. I was just reading over another thread

http://www.mynissanleaf.com/viewtopic.php?f=44&t=14965" onclick="window.open(this.href);return false;

In this post djjazy reported that on Leaf Spy, the SOC was recorded as 0.6% SOC and that his battery capacity was 21.5 kWh (what many others report) which perfectly matched the miles driven divided by the average miles/kWh (I assume as reported on the dash).
I have been turtled with 9% SOC showing on my Leaf Spy and on another day with 11% showing on my Leaf Spy. Thus it seems that the bad cell is preventing me from using the bottom 10% of my battery. Also in the screenshot above, at 100%, LeafSpy is reporting 97%. Is this normal? If not, I'm losing another 3% at the top too. Fully charged, I'm at ~282 Gids, and at turtle ~5 Gids.

When I take my total miles driven and divide by the average miles/kWh for the day, I usually get a number like 20 kWh or lower again indicating that the total capacity of the battery is too low. I haven't done many tests from full charge to turtle...because its not good for the car! But I have MANY test from say 80% to 30% and when you extrapolate those cases to 100-turtle the results are comparable.

One other observation seems to clearly indicate some anomaly which is the rate of charge. Below is some typical data while I'm charging my car (not using Leaf Spy, but only the dash readout for %SOC)
Level 2 charging, Seimens Versacharge
Time %SOC minutes/%SOC gained
2:57 63%
3:11 71% 1.8
3:23 78% 1.7
3:33 87% 1.1
3:44 94% 1.6
3:48 95% 4.0

Now I know that it slows down as you get close to 100%, so maybe this time it slowed down a bit sooner. But what's with the very high rate of charge in the middle?? There is no way that can happen. I've seen this at other times too. The net result is that I think my car does not charge steadily....or more likely the battery is very non-linear in how it holds charge.

GroundHog said:

drees said:

What do the cell-pair voltages look like when the pack is 80% and 100% charged?

Click to expand...

I finally got around to posting this. At 100%, the bad cell is still obvious and would meet the formula criteria. But from what Cliff posted, the minimum cell voltage is too high for the test to be valid and of course the variation is only a small 27 mV.

Click to expand...

I'm not convinced you have a bad cell since cell-pair 25 is not balanced. The real question is why is your LEAF unable to balance cell-pair 25?

Perhaps there is a problem with the shunts...

RegGuheert said:

I finally got around to posting this. At 100%, the bad cell is still obvious and would meet the formula criteria. But from what Cliff posted, the minimum cell voltage is too high for the test to be valid and of course the variation is only a small 27 mV.

Click to expand...

I'm not convinced you have a bad cell since cell-pair 25 is not balanced. The real question is why is your LEAF unable to balance cell-pair 25?

Perhaps there is a problem with the shunts...[/quote]

Sometimes at 100% the cell pair IS balanced. Sometimes not. But it always ends up unbalanced by the time I'm at LBW or VLBW. Of course I don't really want to always charge to 100% and I think the bad cell affects my range even when I don't take it down to LBW, VLBW, or charge to 100%. But when I say my range is not good, my dealer just tells me "well of course, you aren't using the full battery..."

How would I know or determine that there is a problem with the shunts? How is the dealer supposed to determine this?

GroundHog said:

Sometimes at 100% the cell pair IS balanced. Sometimes not. But it always ends up unbalanced by the time I'm at LBW or VLBW.

Click to expand...

If your pack is balanced at 100% (even some of the time), then your shunts are working fine.

drees said:

If your pack is balanced at 100% (even some of the time), then your shunts are working fine.

Click to expand...

Agreed.