RegGuheert
Well-known member
I also greatly appreciate the modeling work that Stoaty has done (with your assistance, I think). I will continue to use that model and may make adjustments as we learn more.surfingslovak said:
I do think there are more than a few reasons for the degradation being worse than predicted by the model. We have discussed many of these before, but I thought it might be good to gather them together here.
Previous summary discussion: 1
1) Nissan's statements to TickTock about degradation rates were not credible at the time they made them. They did not match his level of degradation nor did they match what had already been seen by others. Previous discussion(s): 1
2) Literature searches of long-term calendar battery degradation testing do not indicate a leveling off of capacity loss as the battery fades. Some testing indicates calendar degradation accelerates as the battery capacity degrades. Previous discussion: 1, 2, 3, 4, 5
3) Battery testing often uses constant-SOC charge and discharge endpoints rather than constant-energy discharges as would tend to occur in an electric vehicle. This discrepancy between testing and actual use tends to make battery models optimistic. Previous discussion: 1, 2
4) As LEAF batteries degrade, owners often need to charge to higher SOCs and/or discharge to lower SOCs, either/both of which will tend to increase degradation rates. Previous discussions: (Many, many posts on this forum indicate owners have been forced to charge to 100% due to battery degradation.)
5) It seems that many LEAFs came off the assembly line with "extra" battery capacity beyond what the BMS would use. This was seen by the fact that many owners saw 281 GIDs consistently for a period of time when the car was new. As a result, extrapolations of degradation which included this initial period of "hidden degradation" will tend to be optimistic. Previous discussion: 1
6) The battery temperature management system on the LEAF functions like a track-and-hold for temperature. When you couple this fact with the fact that most LEAF drivers use the car to commute to work, returning home during the hottest part of the day, you end up with LEAF batteries experiencing an average temperature environment which is quite a bit warmer than the average climate where the LEAF is located. Previous discussions: 1, 2, 3, 4
7) I think there is a knock-on effect from the track-and-hold issue above which tends to make it not only affect the calendar losses, but also to increase cycling losses. The point here is that if you drive a LEAF during the heat of the day, the battery will be discharged near the peak temperature of the day. This will tend to cause faster cycling degradation on top of the faster calendar degradation mentioned above.
8) The second knock-on-effect of the track-and-hold thermal management system in the LEAF is that it does not do an effective job of removing heat generated when charging the battery. The result is that the battery will tend to heat up when charged, but will not tend to cool off for a long period. This effect will be most significant at higher charging rates, when charging at higher SOCs and when the vehicle is not driven for many hours following a charge. Previous discussion: 1
9) Many of us keep our LEAFs in our garages, particularly at night. Unfortunately, the garage also tends to operate like a track-and-hold for temperature. When the door is open, the temperature tends to track the outdoor temperature and when it is closed, it tends to hold the temperature. This is particularly true for well-insulated garages, unless they happen to be air-conditioned. Because the cars are often driven into the garage during the heat of the late afternoon, the result is that the temperature environment where the LEAF is stored at night tends to be warmer than the surrounding climate. Previous discussion: 1
10) Nissan apparently forewent some battery features which improve high temperature performance such as ceramic coatings on the separator materials which other manufacturers like LG included in their products. Why they would do that knowing they are marketing a car without an active battery cooling system is entirely beyond me. One would think such omissions should have been baked into their battery estimates, but perhaps they got missed somehow? Previous discussion: 1, 2
Lately I find myself thinking that the number of batteries that Nissan will replace under the battery capacity warranty may be much larger than most of the estimates that I read here. Specifically, it seems to me that anyone who has lost at least one bar in less than 2.5 years and under 25,000 miles will likely lose the other three before the warranty period is up. That might mean people like Stoaty and many other Californians may be included.
As always, time will tell.
Edit: Added a bunch of links to previous discussions on this forum, many of which reference external data.
