It's been a year and a half since I last did an update of the data, so it's clearly time to do so. Anyone who wants to be included in the new update should send me their log files. If you haven't done it before, just DM me and I'll let you know how. If you send me a log and I don't reply it probably went into my spam folder, so also DM me and I'll find it.
I think I haven't posted an update since October, 2019 so I'm really overdue. This includes new data for four cars: 670 (mine), 33, 209 and 1180. The new data for the last two covers about three years. Mostly, things continue apace with maybe a slight flattening of the curve. At the very least it's clearly not going down at the same rate that it did during the first year when it seemed terrifying. Roughly extrapolating the curve, I'll be at the CAC of a new original battery (154) in about two more years give or take. You'll notice a big drop in my CAC around 1410 days. That corresponded to a long-ish drive and came after about a year of pretty flat CAC. This is consistent with the algorithm adjusting things downward when it gets a data point from a low state of charge. It had probably been decaying for the year and just giving (somewhat) optimistic values. The drop looks much steeper on the by-mileage graph. That's further evidence that time is the thing that's mostly responsible for loss of range, and I have been driving much less during the pandemic (15K miles in 2019 and 6K in 2020). Comparing 670 to 33 should make it really clear that the big factor is time. Their CACs are really close to each other each with about 4.5 years on the battery, but 670 has nearly 4x as many miles. Drive your cars! Letting them sit in the garage isn't helping the batteries any. 1810 looks a lot like 33 but with a later install date. 209, however, is somewhat of an outlier on the bad side. I'm not sure what's up there, though I wouldn't be too surprised if it's just rarely range charged, which can cause the algorithm to underestimate the battery capacity. If more folks send in their data I'll do another update, but if not I probably won't do one for at least 6 months to a year. It's not clear it's helpful more often anymore.
Darn not good news with 209, at least she’s with Gruber now due to a PEM board that fried so hopefully I can get them to do a quick check on the battery before sending it back. I hardly range charge it, very rarely do I need the extra juice
Did you guys see this post in the Facebook group? I thought the owner might post here but it seems like in the meantime Tesla agreed to give him a new pack. By the way, I have been too busy to pull the logs in recent weeks. However the car has hardly been driven at all in lockdown and would not likely be a representative CAC. Hopefully I can use it in the summer.
Range charging makes the CAC go up. If you haven't done it much, it might make the CAC go up really a lot. I'm not entirely sure why, but it's probably a combination of two things: the computer gets data on what happens when the battery gets to high SOC and uses it to revise its estimate; and the battery balances. It's not like the cells get healthier from being charged more. The flip side of this is that running the battery to low SOC will cause the CAC to decline. While it's possible that this is because something bad is actually happening to the cells, I think it's much more likely that it's just the computer getting more data and updating its estimate.