Mottyski82 wrote:So let me ask if I understand you correctly... Are you saying that you suggest that before I bring the car in for the next battery check, I charge the car a couple / few cycles using the 100% charge option to better balance the pack. Then, when I have them run the annual battery checkup, I opt for not leaving it there overnight for a free charge, and instead, try to deliver it to them with a SOC where voltages are closer to 3.7v or even 3.6v?
No. As you correctly stated, the annual battery checkup does not include performing the Cell-Voltage Level Inspection (CVLI) test which I have discussed. That test is time-consuming and they will only do it if you report a weak cell. Insteady, the annual battery checkup simply reads data from the vehicle's computer to let them know the condition of the battery and whether or not the customer has been abusing it. It includes things like how many times a charge was initiated above 80% SOC level and how many times the battery temperature got up to seven bars, etc. There is a post around here somewhere in which Ingineer details what the car reports.
Mottyski82 wrote:I try not to allow the pack to sit for hours @ either a low voltage like that or @ a high voltage as a full charge.
Me, too. Our LEAF spends most of its life between 25% and 40% SOC. The downside of this approach is that the pack can get quite out of balance after a few weeks or months of this type of charging. A MY2011/2012 LEAF with an out-of-balance pack can take several charge cycles to 100% to achieve a good balance. MY2013 and beyond can apparently balance in a single charge to 100%. Which model year do you have?
Mottyski82 wrote:In my opinion, this should be exactly what the annual battery checkups should be for / about. Nissan claims that the battery checks are to spot a problem (in the way you are using the car) before it ruins the battery.
I don't disagree, but as I mentioned, the CVLI test likely is a bit too much for a routine test.
Mottyski82 wrote:I suppose, it doesn't exactly sound like they want to identify cells which could be replaced even though they did fail during the warranty period, because that's money out of their pocket. But, replacing those bad cells earlier rather than later could have a major effect on the longevity of the battery pack as a whole! What are EVerybody's ideas on how to go about trying to get these bad cells replaced? After all, that is one thing of beauty about the design of the LEAF battery pack... The ability to fix the battery before the bad cells start to "pull down" the performance of the "whole" pack!!
While I agree that the bad cells do "pull down" the performance of the full pack, I do not agree that bad cells will adversely affect the longevity of the pack as a whole. Rather, I believe that the presence of a "bad" or weak cell or cells tends to *reduce* reduce the stain on the other cells in the pack, causing them to experience lower maximum voltages and higher minimum voltages. This is due to the way the battery management system restricts cell voltages: it limits the maximum and minimum of the highest or lowest cell. Thus the other cells will not reach that level unless the pack is fully balanced. The downside is that the capacity of the pack tends to look like the capacity of the lowest cell-pair times 96, so range is impacted.
All that said, I do not think replacing a weak cell is a panacea. While such a fix can improve the overall capacity of the pack, it will not result in a balanced pack. Rather, the two cell-pairs contained within a module will have more capacity than the rest of the pack and their shunts will work hard to try to keep them in balance with the rest.
To me, the bigger issue is that I do not wish to have the dealer opening our factory-sealed battery pack unless it is really, really necessary. Frankly, what we have seen with our LEAF is mostly due to cell imbalance rather than a weak cell. I do believe cell-pair #37 is a bit weaker than the rest, but that didn't stop me from driving over 69 miles last Friday and arriving home with 34% charge remaining. So while the car's instrumentation is reporting a loss of 16% of the original capacity and a "Health" of only 70%, I'm achieving best-ever (by quite a bit) trip performance out of the vehicle. (And, yes, I understand there are many other factors involved!)
My plan is to continue to drive the car as much as possible and keep an eye on the battery balance and individual cell condition. If any cells get particularly bad, I suspect that will result in rapid loss of capacity bars and the possibility to claim a new battery under the battery capacity warranty. So far I see no obvious signs this will happen. Otherwise, I intend to see how long we can use the vehicle with the original battery and then try to claim a failed cell or cells close to the end of the 8 years/100,000 miles if there are cells which clearly fail the CVLI tests.
As it stands now, I'd prefer to keep our LEAF out of the hands of the dealership if possible. The good news is that with LeafSpy we can easily run the CVLI test ourselves, so we are not fully at the mercy of the our dealerships.
BTW, a single cell which is much weaker than the rest is likely to look similar to the image linked from this post
. Did you case look somewhat like that, or did you have a much bigger spread with the rest of the pack?