The Model S was never designed to be a cheap or easy repair, especially the battery pack. In fact, let's look at some history.
When Tesla designed the S battery pack, it was designed to be 100% non-serviceable. If any component within had an issue, it would need to be replaced entirely.
How do we know this?
Early on, Tesla used contactors within the packs from Tyco that were undersized for the job and failing after relatively short periods, depending on how the car was driven. (Tesla used their telemetry data to determine who drove their vehicles within the limits of these underspec'd components and only replaced them on cars where they figured they would fail instead of, oh I don't know, doing a recall to replace a critical component that doesn't function as designed... story for another time.) At first they were doing full pack swaps, then crating and shipping the original batteries to Fremont in order for the crews there to destructively open the battery packs, replace the contactors with updates components, and then fix and resealing everything.
There was no procedure for this. The batteries were never designed to be opened. The only semi-accessible component was the high-voltage fuse... which still required complete removal of the battery pack to access along with resealing that area.
Eventually, they came up with a rather ridiculous procedure that would take two techs about half a day (plus sealant set time) to perform at a service center in order to replace the failing Tyco contactors. At some point a random service tech in the field came up with a modification to that procedure, including a tool he designed and welded up himself, that helped speed up that whole process down to a couple of hours (plus sealant set time).
They performed this procedure on thousands of Model S over the years... even so, there are still quite a few out there that had never had the "proactive power switch replacement service" performed. I know because we still occasionally get cars with batteries that have these old Tyco contactors in them (usually barely functional and visibly burned from years of overuse).
Let's take the position of the 12V battery on the early S as another example. Tesla never intended for the 12V battery on the S to ever need replacing. Why would it need to be? We've got a giant battery under the car that can handle everything. This 12V should never get used. Let's put it in the least accessible place in the car!
This may have worked out for them, but early on customers complained of excessive vampire drain. The 12V was going to last forever, because the car rarely ever "slept." Instead, it'd sit there most of the time with the contactors closed, DC-DC converter active, its cooling pump running slowly, and other wasteful things pulling anywhere from 30-80 watts continuously. So, 3 to 7 miles of vampire drain on a good day, not even counting any of the early MCU sleep issues that could easily triple this.
Eventually Tesla tweaked the sleep setups of the MCU and BMS to disengage more things. This lead to a bit more wear on the undersized 12V battery... leading to early failures. This was before "12V battery needs to be replaced" warnings. Your warning would be that your car wouldn't unlock in the morning, wouldn't open, and otherwise would be non-responsive.
There wasn't a service procedure for replacing the 12V battery yet.
When they had to come up with one, the positioning is so ridiculous that it involves removing the windshield wipers, several pieces of underhood trim, the air filter and its box, an entire fuse block (disconnecting and labeling every one of the dozen+ wires first), and then after all of that, making a makeshift handle out of duct tape (yes, this is in the original official procedure) in order to help pull the 12V out of position, then a series of maneuvers to squeeze it through a spot never intended to be used for this purpose....... then do it all in reverse to install the new one. Time? At least an hour.
Battery swaps? LOL. That was doomed from day one. Yes, they clearly intended for these to be machine swappable. The connector designs and such are actually quite good with this in mind. In practice, however, not so great. The alignment of these connectors is never perfect. They're on springs, and any dirt/grit that gets into the wrong place will prevent them from fully engaging. A misalignment by just a couple of mm can actually cause a connector to break upon reinstall. Any automated setup would need to remove the battery, clean and align the connectors, install the new pack, and double check the seating of the connector. That last part is probably what killed swap stations. Automating that is probably impossible. Heck, it's difficult for humans even with the rear aero shield removed, let alone with nothing but the battery out. Good idea, but just not going to happen. Plus the logistics of it are too much of a nightmare. We've gotten enough cars in over the years with "Service Loaner" batteries to know that Tesla has no way of recovering a battery once its installed in a car.
Could go on and on, but let's fast forward a bit.
Today, the 12V batteries are way more accessible. Still not as easy as some ICE cars, but not objectively the worst possible replacement procedure ever conceived anymore.
No battery pack made after 2014 could ever hope to be automatically swapped at all, as the design changed sufficiently to kill automation. Then in 2016 the car-side connectors were completely changed and have zero play for alignment, requiring monitoring from the side upon install, which isn't possible with all panels in place. Then we have the Model 3, Y, and now the Plaid series... all of which have batteries that can't be removed at all without performing procedures on the inside of the car. Quick and easy battery swaps are dead dead dead dead.
The battery packs were updated to be slightly more serviceable in 2015. The rear are that houses the BMS, contactors, and other electronics was now accessible without destructive disassembly. The removal of the battery is still required, thought. The HV fuse panel was also flipped to the underside of the battery pack... meaning the fuse can now be replaced without removing the battery pack, if needed.
All of this said, there's one major point with regard to the battery packs: The batteries themselves were never intended to be replaced or repaired, and still are not. The only reason that the Model S was designed with manageable sized modules was ease of manufacturing, and less loss if they were to screw one up at build time (which seems to have happened a lot). If they had started with a Model 3-like monolithic module design, Tesla likely would have went bankrupt from failed modules since the process had not been perfected.
The module design within the battery does NOT mean these are individually replaceable. This was never intended, and does not work. This is not the design, and there are no exceptions. From a technical perspective, it's not possible either. (I've written about this many times, and noted more below.)
Tesla has always, from day 1, intended for the entire battery pack to be replaced in the event of any issue. And they stick to this, leading to very high costs to replace. Tesla's prices are actually very high because they give almost no value for the core battery pack, either. So with Tesla, after labor and parts, in a best case scenario you're looking at just under $14k or so for a replacement service.
At 057, we've streamlined this as best possible. For a like replacement, the customer generally ends up paying $4k to $6k, depending on the actual issue. It's not because we've got some secret that makes the process cheaper, either. The labor is still the same. The difference is that we're not screwing the customer out of core value since we have a network of customers who repurpose the recoverable parts of these batteries for other projects (mainly off-grid solar projects). Whatever value we're able to recover from the customer's core battery we pass on to the customer. Simple as that. The result is that the customer gets a fully working replacement battery at the lowest cost possible.
There are some repairable failures, all involving electronics within the battery pack. But there are no repairable failures involving the battery modules themselves. If a cell or cell group has failed or has issues, this isn't repairable. Despite claims by Youtubers and other companies, you simply can't butcher a module and remove a cell, or replace a module with another from another car, and then expect it to work fine indefinitely. Instead, that battery will be struggling from the moment it's reactivated... eventually and inevitably failing again. Sure, it may work for a while. Days, maybe even a year if you're lucky. But it will fail. These "repairs" are garbage and should never be done.
Trust me, if it could be done cheaper, we'd be doing it cheaper. We do several per week at this point, and it's definitely not a high margin prospect. In fact, it ties up a lot of capital doing full replacements at an invoice price way lower than the cost of a replacement. If we could do this as a service that didn't involve $30,000 to $60,000 in components floating around for each vehicle (replacement pack and core pack)... we'd jump on that in a heartbeat. Unfortunately, it's not possible.
Anyway, there's your history lesson and reasoning on why pack replacements will very likely never be any cheaper than they are now. In fact, with the Model 3,Y and Plaid, they're likely always going to be worse since these packs have limited to no secondhand value once failed, unlike the pre-Plaid S/X packs.
