So here's a hypothesis. The CAC algorithm doesn't get any data unless you range charge the car or run it to very low SOC. Otherwise, it's a complete guess based on what the engineers thought when they wrote the code. When you DO range charge or run to low SOC, it gets some data, but it averages that in with what it already thinks (which may be based on old data, or may be based on lots of guessing).
The guesses that it makes are essentially just drawing a line from when it was new to the current time. However, when it gets new data from a range charge, it not only adjusts the CAC, it adjusts its estimate of the slope of the line. So, range charging not only increases the CAC, it decreases its rate of decline. Again, this isn't saying that it helps the cells (it almost certainly doesn't), it's that it helps the estimate.
As evidence of this, I made the following chart. It's really simple. I just pulled the CAC-vs-miles chart for my car (#670). Then, I chose four range charges that I did (usually really several in a row) that made the CAC go up. Then, I drew straight lines from the starting CAC and 0 miles through the peaks. The fact that the CAC more-or-less follows the lines until I start range charging again fits the hypothesis reasonably well.
So then that lets us ask what the real degradation curve looks like. For that, I just drew a smoothed line through the same peaks. This gives the second graph. And *that* graph shows a strong suggestion of the degradation rate slowing down. Of cells that lose some capacity and then stop getting worse for a while. This, of course, is only one car with four data points. Furthermore, I range charge much more often than I run the battery down to low SOC, so the algorithm is only seeing the top of the battery, and we're not all that sure what's happening with the bottom. Still, less discouraging than news usually is in this thread.
This should also make it obvious why I really want someone else who's got a car with low CAC and range charge it for a number of days in a row, until the CAC stops climbing. If it winds up somewhere near my smoothed curve, then maybe we're on to something. You don't have to drive the car too much, just let it range charge a number of times in a row. It didn't kill my battery, it probably won't kill yours.
The guesses that it makes are essentially just drawing a line from when it was new to the current time. However, when it gets new data from a range charge, it not only adjusts the CAC, it adjusts its estimate of the slope of the line. So, range charging not only increases the CAC, it decreases its rate of decline. Again, this isn't saying that it helps the cells (it almost certainly doesn't), it's that it helps the estimate.
As evidence of this, I made the following chart. It's really simple. I just pulled the CAC-vs-miles chart for my car (#670). Then, I chose four range charges that I did (usually really several in a row) that made the CAC go up. Then, I drew straight lines from the starting CAC and 0 miles through the peaks. The fact that the CAC more-or-less follows the lines until I start range charging again fits the hypothesis reasonably well.
So then that lets us ask what the real degradation curve looks like. For that, I just drew a smoothed line through the same peaks. This gives the second graph. And *that* graph shows a strong suggestion of the degradation rate slowing down. Of cells that lose some capacity and then stop getting worse for a while. This, of course, is only one car with four data points. Furthermore, I range charge much more often than I run the battery down to low SOC, so the algorithm is only seeing the top of the battery, and we're not all that sure what's happening with the bottom. Still, less discouraging than news usually is in this thread.
This should also make it obvious why I really want someone else who's got a car with low CAC and range charge it for a number of days in a row, until the CAC stops climbing. If it winds up somewhere near my smoothed curve, then maybe we're on to something. You don't have to drive the car too much, just let it range charge a number of times in a row. It didn't kill my battery, it probably won't kill yours.
