I had an appointment with the Dublin SC for tomorrow, Fri, about my battery seemingly losing too-much range/capacity, but late yesterday I got a call from a Tesla "lead technician" who talked with me for the better part of 45 minutes and persuaded me that there wasn't anything wrong or broken (bad cells) with my battery. I know Tesla employees can say various things that turn out to have varying levels of accuracy/veracity, but I'll relay what William (that's his name) told me:
Let's start with , some asides/interesting things he said:
1. First, he said he's Dublin's Lead Technician (or maybe one of them?), and he was calling customers with upcoming appointments who indicated issues that they felt might be ones that could be resolved over the phone. There apparently is a "backlog" of repair/maintenance requests, and he was enlisted to help reduce it. (So, Pro-Tip A: If you want Tesla to call *you* about your issue, make an appointment to physically bring your car in for a look-see. Doing this is the sole reason I got a call from this technician and got to have him look at my car remotely. But, there this pro-tip B: Take Their Call when they call you. If they leave a message, they ask you to call them at the general number, which leads to HUGE hold times (see Item 2. below), and generally you won't get the actual guy who called you right away on the phone. This is what happened to me at first, before this technician called me, so this was the second call from a tech I got.)
2. As a slight aside, I also told him that l was glad he called me, because every time I call the Dublin service center, I get pushed out to a national queue and put on hold for up to an hour (and no less than 30 minutes), and sometimes I've just hung up because life got in the way and I couldn't stay on hold that long. He apologized and said indeed they have very long wait times these days and it's something he hoped they fix soon. He did attribute it to the large numbers of 3's (and S's and X's) that are coming on line these days - not a surprise really. (I say all this in case anyone else has experienced the near-impossibility of actually talking to a local person in their local SC). Anyway, that's that.
3. He verified to me that indeed they can remotely look at Model 3 battery packs, just as they can look at S or X ones. This was important to me because I was told a couple of weeks ago by a cust. sv. guy at Dublin that they cannot remotely access Model 3 battery packs or do any remote analysis on them, which I thought sounded way wrong, but that's what he said.. This guy William said ineed this was just wrong. William proceeded to prove this to me by bringing up my car on his computer, and actually accessing my battery, and ran a few analytic programs on the data he pulled from my battery - all while I was on the phone with him.
OK, here's the good stuff:
4. He said that the displayed range, and the displayed SOC remaining, is the result of a pretty complex algorithm (I'm sure most on these forums know or figured this was true, but anyway, nice to hear it from a "lead technician" at Tesla), and that actually the SOC displayed is an average (a little more than just a straight average, he said, but one can think of it as an average) number, based on the system looking at the SOC's of each of the battery packs in the car. He said the first numbers he looks at when delving into someone's battery pack is the "minimum SOC" number, which is the pack with the lowest SOC, and then the "maximum SOC" number, which is the pack with the highest SOC. A healthy battery pack will have a high/low SOC differential that is pretty small, within a .1 V he said (I think it was measured that way - he spoke really quickly. Maybe it was .01? Anyway, I was doing my best and couldn't take notes at the time, unfortunately). He said the recent readings from my pack showed a SOW high/low difference of no more than .1V (or .01V?), which he said was excellent, a very well-balanced and therefore healthy pack.
5. He also said that this high/low SOC measurement was the "balancing" thing that folks talk about, where if the Low/High SOC starts to diverge too much, the car will stop charging when the higher SOC packs reach full SOC, or targeted SOC, but then the ones that are on the lower end of your overall pack's SOC at that point in time would then not get charged to a higher state of charge (because the charging will be stopped when the higher SOC ones hit the level, even if the other packs at the lower end of the SOC spectrum are not charged fully or to the set SOC target). Essentially charging stops when the highest SOC packs hit the target SOC level, leaving the lower SOC packs at a relatively lower SOC, which can reduce range. He said that a typical indication that SOC high/low is unusually large/off, is that your car starts to cease charging prematurely, before your set SOC is reached.
6. He said also that if the pack had any real problems - like cells going out, or even severely out of balance - the pack would "start to throw errors remotely" to Tesla, and they typically would be reaching out to an owner of such a problem battery pack well before the owner even saw any adverse effects / reduced range, as a result of such errors that were being transmitting. He said any such errors my battery would have shown would be on my car's chronological "error log", which he then proceeded to check whilst we were on the phone. He said I have no such battery-related errors, though he correctly noted that my most recent error is a "low windshield wiper fluid" error, which indeed I have seen on my car (so he definitely was looking at my car's error log!) It's nice to know that the BMS is apparently set up to throw notifications to Tesla in the event of bad cells or other battery problems, and that mine has yet to do this.
(PS - Asked and Answered: there is no recommended wiper fluid - use your favorite . . .)
7. Probably the most notable thing he said, was that indeed charging to lower SOC's (like the 70% I was typically doing), and then using only 10-15% or so (ie, driving not a lot on a daily basis, 30-60 miles, which is what I do) will in fact tend cause the system to start giving lower total range numbers, as the BMS and the software calculating that range will have less info with which to extrapolate the range. So, essentially he is saying that keeping your SOC low (70-75%, as I have been doing) may well result in a lower total displayed range, but that's going to be in large part not due to a bad battery but due to the BMS having problems with the range estimation due to lower SOC and range used.
8. The good news is he said that indeed the 10-100% cycle charging can raise this stated range, though if you go back down to a regular/daily 70% SOC charging regime, it's likely that the overall range displayed will drop again.
9. I asked if it's OK to keep the car at 90-ish% SOC on a daily basis, even if I'm only driving no more than 40-ish miles on any given week/workday, and he said that it is fine, and that may well result in a bit higher stated range as well (which is what I was experiencing - when I went from a daily 70% SOC setting to a daily 90% SOC, my displayed/calculated full range went from 288-ish to 300-ish). He did say it's also fine, and perhaps long-term a little (just a little, maybe, he said) healthier for the battery, to keep it at a 70-80% SOC daily, but just realize if you do this your overall range displayed probably will drop a bit, though your actual range isn't dropping - it's just the calculations of range that the system does, becomes trickier / less accurate when you keep your daily SOC lower, as in 70-ish% SOC.
10. Lastly, he did reiterate and confirm the general degradation pattern we've all heard/read about for these batteries: You'll see a drop in range initially, around 5%, over the first year/12k miles, some of which will in fact be degradation, but then you'll see that drop slow and practically stop and stabilize for years after this.
What this all means to me, is with the L/R stated range of 310 when new, most can expect that total range to drop to 290-300 miles within a year (5% of 310 = 15.5 miles, so that'd put the true Rated Range at 294-ish after one year / 12k miles) and then virtually stabilize after that, with very small and slow degradation drops after that for years to come. (SideNote, He said at least twice in our conversation that the older S's he sees, including his own, indeed seem to level off for years at around 90%, give or take - some after 200k miles even.)
So, some lucky folks will keep 300-plus after a year, but probably most of us 3 folks won't, but that's ok. And don't worry unless you start to see consistent drops into 280 (or below) range in the first year, even after 90% SOC charging and/or 10-100% cycling a few times. And if your battery actually is dropping cells or otherwise failing, it should be throwing errors to Tesla and you should hear about it. Lastly, if you're concerned still, then brave the long hold times and somehow get ahold of a technician and insist that they look at your battery while you're on the phone with them. They should be able to tell you if your high/low SOC's is at a worrisome state and otherwise give you some better insight into the state of your pack.
Bottom line, I felt reassured that my battery isn't defective, and I canceled my in-person appointment that was set for tomorrow. I'll probably charge to 90% daily for a while, knowing that's not going to discernibly harm the battery, and then just monitor the situation.
Sorry for the TLDR post. Just felt folks might want to know as much as possible about this battery thing, as heard from a real, live "Lead Technician" at a SC.
