Hi,
I also own a S85 with about 75.000 miles, but it lost only about 5 miles after the update, so far.
I think
degradation of the battery wasn't defined very well, so far.
We all thought that the current amount of energy available at full charge of 4,2 V divided by the amount of energy of a new battery charged to 4,2 V subtracted from 1 and multiplied by 100 will be the degradation in percent. In pure physical terms this may be true, but technically this doesn't take the internal chemical changes in the battery into account, that have influence on usability (internal resistance) and safety (lithium plating). Up to the firmware update, causing a drastically lower range being displayed, it seems to be that Tesla, when calculating the state-of-health of the battery in form of the capacity for full charge, didn't take the usability and safety much into account. So over time the lithium plating of the cells, caused by high charge power at high SOC and low battery temperature, is increasing more and more, until the separator is punctured, causing internal shorts and my finally cause battery fire. That this happened only a few times up to now, even there are billions of cells in use, is a wonder. This shows that Tesla has done a good job in improving the BMS over time. The last changes definitely go into the same direction.
As has been already written, Tesla may now detect the health of the battery regarding safety better, by detecting the lithium plating through differential voltage analysis, when charging to 100 %. If the voltage starts to rise with a higher slope than normal, charging is stopped. The reason for this sharp rise is that the lithium ions cannot be intercalated into the graphite anode fast enough, which finally increase lithium plating further.
So I agree with those that say that the degradation (capacity, usability and safety) was already there. We just didn't see it until Tesla introduced the new software. In my opinion Tesla is not at fault regarding making the real degradation visible here, but it is certainly at fault regarding the missing communication. If only a few owners are hit very hard, by losing more than 10 % of there range, then it should be also possible to replace the batteries by refurbished ones. The parameters should be transparent.
Taking this into account, I can only warn people to constantly test the battery capacity with 100 % charges. They may make the situation even worse, because nobody knows if Tesla is already stopping charging early enough to prevent further lithium plating. It is better to use either ScanMyTesla or TM-Spy to read out the BMS values, but charging to lower SOC and dividing the displayed range by the SOC percentage, will also be good enough.
How can the risk of lithium plating reduced?
- Don't charge to high SOC
- Don't charge when battery is cold
- Don't charge with range mode on when battery is cold
Charging in summer with warm battery is not that much of a problem. Just charge immediately before a road trip to the SOC that is required.
In winter it is better to charge immediately after the trip, when the battery is still warm. But avoid charging to more than 80 % if possible.
Keeping the car at SOC of 10 - 20 % most of the time, gives the chance to reverse lithium plating a bit.
BTW, I don't see the loss of capacity and the lower charge rates at the SuC as separate issues. Both work together in reducing the chance of lithium plating. So at least all owners of vehicles with S85 cell type may have to live with more visible degradation and lower charge rates.
Finally, I think this problem will not be that visible with cells with silicon in the anode, because there can the lithium ions be intercalated more easily.
I hope this helps,
Emil
