Replacement Battery with low cell Voltages

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Marktm

Marktm

Well-known member
Leaf Supporting Member
Joined
Jan 21, 2016
Messages
854
Location
Houston, TX
Battery was replaced in early November (under warranty) and has already lost about 3% (varies) amp-hours and HX. What is concerning is the last quadrant of cells (73-96) consistently have the lowest voltages. Attached is the near-depleted voltage ranges. I understand this "magnifies" the deltas, but over 110 mv?? Normally at full charge the delta is 20-30 mv.

Should I question Nissan about a "bad" replacement - mainly to get the "problem" on record? - or is this to be expected?

IMG_4859.PNG
 
What have you got to lose by bringing it to their attention. At the least, you would get peace of mind.
 
Looks normal. You have to have dozens of deep cycles.
Set your charge limit to 100% for a month. Go at least down to 20%.
It will level out with weeks.
Also your SOH and Hx will fall rapidly down to level it was before cells failed.
 
sendler2112 said:
What does it look like at the top of a full charge after a 100% disconnect?
Click to expand...
This is the profile at 278 GIDs. The new battery has had at least a half dozen "full" charges with several taken to VLBW - all level 2. The same cells (73-9) have always determined the max delta mv.

IMG_4835.PNG
 
Ok. You have to continue cycling the battery.
Interesting, that cells that are new are at lower voltage AND are shunted to discharge.
That doesn't make sense. Every other cell should be red, and those low voltage cells blue.

Just for a test run it down to turtle, aka 0.5kWh left. Make some screenshots.
Be near the home. After running down to 0,6 go home and run heater at max.
Take some screenshots. Leaf will die. Then make another screenshots and start L2 charge
immediately.
I would recommend doing it when battery is below 7 temperature bars.
Also battery must be at least 15C (all sensors) aka 59F converted. (otherwise Hx SOH update will not happen)
Charge to 100%.

Leaf should die when one of the cellpairs falls down to 2.6V.
 
It might force BMS to balance harder/faster.
BMS only sees cellpair voltages. It takes that data to balance them.

Do not baby the battery. I hope you already noticed that doesn't help.

Voltage delta should get smaller over weeks. Also if new cells are more degraded
then they will be depleted earlier. Therefore pack will never get balanced.
If new cells are in better health all other cells will run out of juice earlier.

My battery is in very good health. Voltage delta at full charge is less than 10mV.
When pack is really empty delta is as high as 400mV.

https://goo.gl/photos/xxzQQZgzxPtXbxPV9
 
The packs only balance when the highest cells are shunting at the top while the charge is still connected. Constantly taking the pack to the very bottom will just take the imbalance to the maximum. This is a warranty replacement pack that Nissan just put in for free. They are not going to do anything else for this car unless a MIL light pops on.
 
arnis said:
My battery is in very good health. Voltage delta at full charge is less than 10mV.
When pack is really empty delta is as high as 400mV.
Click to expand...

Seems very high delta mv, but obviously it is highly variable with the SOC of the battery. Is there an "alarm" point of delta mv that will set an error code in the system - and does it take the SOC into consideration?
 
It just seems that way. From 3V to 2.6V there is hardly a percent of capacity difference.
It translates to 0,01V difference at top end. Aka same capacity difference (a percent).

If any cellpair drops below 2.5V it kills the contactor. Even during acceleration. This is why
power bubbles disappear a mile before dead.
 
Update - new battery has about 1200 miles on it and about 1-1/2 months. AH has dropped from 66.14 to 63. SOH dropped to 98%. Temp bars always mid-range, one QC, one "VLBW". At this rate, a I'll be back to my old batteries final reading of 43 AH in a little over a year.

I'd guess that as the pack balances better this will level off - but no sign yet.
 
Marktm said:
Update - new battery has about 1200 miles on it and about 1-1/2 months. AH has dropped from 66.14 to 63. SOH dropped to 98%. Temp bars always mid-range, one QC, one "VLBW". At this rate, a I'll be back to my old batteries final reading of 43 AH in a little over a year.
I'd guess that as the pack balances better this will level off - but no sign yet.
Click to expand...
Mark,
Please note that the fabled 66.14Ah is just a magic number, not actual capacity of the battery, but rather something that gets programmed into the BMS as a starting point. Initial change can be fast, due to BMS learning the *real* capacity of the pack. Once that is found, degradation follows its normal course.
Cor.
 
Yes, I've found that the AHrs and SOH has varied quite a bit since the new battery in place - went through a period of rapid drops and then would recover. I have a section of (10) cells that are about consistently 20 mv (after a full charge) below all the other cells. The lowest mv range I've seen is 24. I don't know if that is common, but makes me wonder if the original cells were not well selected or it just takes more time to "balance" properly.
 
Try changing the shunt order to 8421 in Leaf Spy settings and see if it then shows the higher cells being shunted instead of the lower ones. I had 160 mV difference deep into VLBW last night and 16 mV difference at full charge this morning on my 2015 so I'm not too concerned to see 112 mV difference in your first screenshot. I suggest you drive and charge as you need and see if the cells balance better after more cycles.
 
@marktm,
You may find a thread from a few months ago informative that described a manufacturing defect in a new 2017 car. A couple cells were defective from the get go and IIRC voltage deltas over 200 mv easily logged. I don't think a MIL was ever set.

I agree with an earlier poster that Nissan is not going to care. You can keep logging for your own interest and ours, or just drive the car and hope for the best. My fingers are crossed that this sorts itself out, and that it is not a harbinger of what to expect in future replacement packs but Nissan's history leaves me antsy on your behalf.
 
Update on 11/3/16 battery replacement:
5/3/17:
64.76 ahrs
100.00 SOH
97.15 HX
386.07 VDC
222 GIDS
32539 miles (~2800 miles on new battery)

Appears things have settled down and "Lizard" is alive and well.
 

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