I actually never expected that my EV battery would last 15 to 20 years when I bought my cars.. I would be fine with 100k miles and 8 years.
What I expected though is that replacement batteries would be a no available reasonably priced after 8 years. For all I computed the gas and maintenance savings and free charging would be worth it.
Is any battery technology even feasible that would last 15 years even with little miles?
100,000 miles is nothing, neither is 8 years.
As we don't really have any vehicles to compare our cars batteries to, lets compare to my own equipment and tools and computers that I have that are aging. (Hang in with me on this)
My first laptop, Received on October 21, 1998. I still have it. It still works, and use it for retro computer games on Windows 1998 SE. It spent most of its useful life on battery. It's mostly been stored since 2008 when the LCD screen's backlight burned out. The lithium battery was stored at ~50% SOC. I haven't touched it in about 3 years. So for the purpose of this discussion, I just went and powered it on. Other than a low clock battery warning (A CR2032 cell, same as in the Model S FOB), still had 38% battery power after that storage. The original battery remembers. I did benchmark the batter before storage, and it was holding about 80% of it's designed (LABEL) capacity.
My moms old laptop, a older than my first one, Toshiba Sattelite 2032, originally Windows 95 upgraded to 1998, it's a POS, but had serial ports, so I used them for programming electric car motor controllers. I still use it every few months. Improperly stored on a shelf in my garage. Battery still holds about 60% of its original charge after 23 years. Also spent most of its life on battery power then recharged.
My cordless Craftsman NexTec drills. When I had my Motorcycle & Electric Car shop, I had one setup as a screw gun, the other as a socket driver. Both would be drained once-two times/day, and they even had a drill equivalent of a supercharger, that would get me 25% charge in 2 minutes. These are small 12v drills, 3x 18650 cells. HARD and HEAVY use for a solid 4 years before I closed my shop down. I still have and use these drills at least a couple times/week. Still original batteries. I also use the same batteries on a portable shop vac, oscillating multi-tool and auto hammer. Cells are rated at 1.5 ah, and as of last summer, the 9/10 year old cells still test out on my benchmark unit at 1.3ah. Not bad at all.
My home Vacuum, Hoover 18v something or other, cant remember the exact name, excellent vacuum until wife demanded a Dyson V10 this past summer for her birthday (Gave the Hoover to my mom). About 6 years old. Battery discharged once/day to once/two days. And those batteries got pretty hot if you ran it the full cycle. Never benchmarked, but run time was about 20 minutes when new, and was about 18 minutes when I gave them to my mom.
My old Dell Mini 9 Netbook. Tiny little bugger, but so so useful, had full install of XP on it. Used the heck out of that at my shop, as it was small enough to fit in the pocket of my cargo pants. During the summer months, it would be on the battery from 10 am to 5pm, from May-mid September. Got it in 2008 as a special Dell deal. That battery held with that use for 3 years. 100% Charge then about 10% left when it got plugged in before closing for the evening. Now, this one was a special case. The BATTERY was still good, HOWEVER, Dell programmed in planned obsolescence. After XX to -XXX number of battery cycles, it would artificially reduce battery capacity, until eventually, it would not run off battery at all. After it finally got to that point where it would not run off battery at all, at about 5 year mark, I opened the battery pack, 4x 18650 cells, and benchmarked AND load-tested each one. Well WTF, tested at 95% of the label's stated capacity! What a crock of crap... Got replacement after market battery for it, one that did not have that planned obsolesce in it, and it's been good to go ever since. I use it now for monitoring my Bitcoin miners. At idle, it only draws 1-2 watts, at full usage, about 10 watts. Intel Atom, amazing processors!
My WORX lawn tools, 20v batteries, going on 6 years with them, still chugging away. No noticeable runtime loss. I can tell as the smaller battery is enough to do my front sidewalk with my trimmer, and just barely use the blower to blow the trimmings, and timing when it runs out of power is just about the same. The Medium battery I have is enough to trim my 7 1/2" Ride on railroad train track in the back yard, go all the way around twice, to trim the grass growing on each rail (450 ft of track, so 900 ft of trimming to go around twice). The LARGE battery is enough for my Jawsaw to cut a cord of firewood, and then blow the sawdust onto the lawn when done before it's dead, and still holding. Heavily used tools and batteries.
My Sunjoe/Snowjoe tools & batteries. I use the living heck out of my Sunjoe 40v 16' chainsaw all summer. Parents have a motel on a lake in the midwest's largest tourist city, Wisconsin Dells, and they provide a campfire each night. So I cut ALL the wood with my Sunjoe chainsaw. Probably 20-30 cords of wood/summer from May through end of September, then also cut my own firewood for the winter (Yes, I use all already downed wood from storms, tree trimmers etc... for both home and the Motel. The area gets a lot of downed trees after storms, so firewoods a plenty!). Now, the same batteries work for my Snowjoe Snowblower. So all winter, I use a combination of my chainsaw, and my snowblower. Same batteries, going on 6 years. I tested each one down to the watt-hour for capacity when new. after 6 years, each of my two batteries has lost about 20 Watt-Hours.
So, what was the purpose of this huge post? Heres my point.
Tesla batteries, realistically, are BABIED in comparison to other batteries. With the BMS controlling temperatures, both keeping the batteries cool, and warm as needed. Keeping the cells balanced and in their happy place. Controlling charge rates more logically from start to finish. And also the sheer number of cells, keeping the demand on any single cell fairly low except in the most demanding of situations (Such as Wide Open Throttle), these cells are well taken care of. Sure they are in a car, but compare to even a cordless drill battery. It's thrown carelessly in a tool bad, dropped on the concrete, run and run and run until HOT HOT HOT.
Heck, even supercharging isn't REALLY the most stressful thing on these batteries. Commenting based on the older 120kW charge rate, not the newer 250kW whatever. Based on the 120kW charge rate, a 85kWh or 90kWh pack, each cell is getting charged at 16-17 Watt at PEAK charge rate. Heck, my 12v Nextec drill charger charges at 15 watt/cell, at normal charge rate, and if I hit that boost button, we're looking at about 41-45 watt/cell for a solid two minutes (At about 125 watt output to boost charge the 3 cell pack) with No Thermal Management what so ever.
Based on how well taken care of a Tesla pack is supposed to be, other than a manufacturing defect, if the BMS does it's JOB, I would expect at least 20 years of USEABLE decent range and performance out of my pack and 400-500,000 miles before I should even need to consider a replacement.
WIth low mileage, if stored or kept at a lower, say, 50-70% SOC, I personally don't see why someone couldn't expect 20-30 years out of the pack, barring manufacturing defect, or component failure elsewhere. The cells are supposed to be formulated for EV use, and the demands of a EV. And at the price point of these vehicles, and the ground up design for their purpose, I don't think I'm too far out there in thinking that.
/End_Caffine_Fuled_Rant_That_Was_Sparked_By_Something_Completly_Unrelated_To_The_Quoted_Post_Apologies