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IIRC, the original idea was that they would pull older batteries from circulation when their capacities dipped, and then repurpose them as powerwalls, an application where weight is irrelevant.

This was back when they expected the batteries to plateau at ~80% capacity after a few years, and they had battery swapping on the roadmap, so they needed to plan for a future where they had a steady supply of batteries that car customers did not want.

The idea took hold, but the batteries lasted longer and swapping didn't pan out, so now they are competing with themselves for battery supply.

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Electric car battery degradation has been super interesting, in that they are going way further than people thought they might. Jonny Smith on youtube bought a 300k+ mile Tesla and the battery is at like 75% health.

As far as I can tell if your battery isn't air cooled, it can go a very long way

There was some research[1] that strongly suggested that varied use makes them last much longer than the steady use that most battery tests do. That is, bursts of high-current draw followed by moderate draw etc vs the constant current load typically used when evaluating battery performance. From the paper:

Specifically, for the same average current and voltage window, varying the dynamic discharge profile led to an increase of up to 38% in equivalent full cycles at end of life.

This was unexpected, hence explains why they fared better than predicted.

[1]: https://www.nature.com/articles/s41560-024-01675-8 Dynamic cycling enhances battery lifetime (open access)

Huh, unexpected is right. Bursts of heavy usage being better for longevity than steady usage goes against pretty much all conventional engineering wisdom.

Without knowing anything about it, I would posit that degradation accelerates the longer the battery is kept above some threshold temperature.

So, a heavy-burst+low results in a sudden high temperature then settling into a lower temperature. Steady flow keeps it at moderate temperature (above threshold) for a long time.

The paper notes there are multiple degradation mechanisms at play, and they are influenced by different factors, such as age, cycles, depth of discharge, state of charge at rest and so on. Hence the non-trivial response to more realistic discharge curves.

However they also note more material studies are needed to understand these mechanisms better.

Any idea why swapping didn't pan out for Tesla? My understanding is they are doing that in China.

What do you mean? It did pan out for Tesla. Faking a single demo granted them 75% more ZEV emissions credit government subsidys [1]. That increased their profits by hundreds of millions of dollars.

All they had to do was go on stage and “swap” a battery without any clear video of the process and never “demonstrate” it ever again.

This is a company known for faking prominent demos like the FSD demo (where it crashed into a wall during filming), the solar roof demo (where they used regular roof tiles and claimed they were solar panels), the optimus demo (where they were teleoperated), etc.

Assuming they even did a battery swap, for which the official demo presents no clear video evidence, preferring overhead views over a close-up of the process or a glass enclosure to see the inner workings, it was at best a one-off custom-made device at the time. The one battery-swap station they claim existed has zero stories of any actual battery swaps, instead only evidence of it operating as a regular Supercharger [2].

[1] https://thewaroncars.org/episode-88-tesla-is-a-fraud-with-ed...

[2] https://slate.com/technology/2022/05/elon-musk-tesla-twitter...

They didn’t fake the demo, but the legislature quickly rewrote the law because it was intended to give Toyota ZEV credits for hydrogen cars.

Tesla did briefly operate a swap station at the site of the Harris Ranch Supercharger until California changed the rules.

There are several reports from people who used it on teslamotorsclub.com, and I saw it with my own eyes.

Hilarious that your source is Ed Neidermeyer. Perhaps the only thing more impressive than Elon’s lies about the state of self driving are Ed’s lies about how Tesla is going bankrupt Any Day Now.

It’s ok though, Ed’s stock manipulation antics enabled me to stuff my IRA with Tesla shares (since sold, when Elon went nuts) and make a nice little headway on my retirement savings.

Cool. Then if you are not lying, then it should be easy to present a clear video demonstrating the automatic battery swapping machine in action and swapping out a battery in 90 seconds as claimed in the demo.

Battery swap was and remains really risky for anyone doing it. You're taking a $10k asset, and swapping it for another $10k asset of unknown provenance. Does anyone really want to be in a situation where they purchase a new Tesla with a brand new, max-range battery pack, then swap it once on a road trip and get one that's been used for 300k miles and is at 75% of original capacity?

The bigger risk is you need a standard battery pack. Sure you can put 3 in a truck or something, but you lose all the space that a standard battery size wouldn't fit but you can cram a cell in. Electric car design is about stuffing batteries where there is space - you need a lot of cells, but the individual cells are small.

> of unknown provenance

I don't understand the comment. Of course they know where the batteries come from. They know everything about the battery.

As long as you can always swap your battery again I don't see the problem

As long as the average battery health in the system is like 90% and the minimum is say 80% why would you care if you're getting a new battery every few days?

If anything it removes a big cause of depreciation from your car

That is fine if you always are swapping. However if you normally charge at home that becomes a big deal - if your current battery wears out/fails because it has 500,000k miles on it are you out a new one? Do you pay for the tow to get to a swap station? Again, if everyone always swapped this would be easy to amortize and not a problem but the mixed use.

Of course this isn't a new problem. I know people who own their own welding gas tank - but they always swap the tank out. The place they swap at somehow handles when the tank needs to be re-certified - and people don't ask questions.

Eh?

In some mysterious future where swapping EV batteries during a road trip is a normal activity, then the battery packs won't be living in a vacuum -- their status can be known. Whether it is known by reading the pack's own electronics, by status reports from connected vehicles and charging stations, by direct measurement, or by some combination of these things: The status is knowable. It doesn't have to be a big ball of mystery.

How much value the marketplace finds in this health status is a different question. And this question is one that we cannot yet know the answer to -- this is not a reality that we presently live in.

We can speculate about how that potential future may be shaped, but that kind of speculation is kind of meritless since that version of the future may never actually happen (and at the present, it sure does seem very unlikely to happen any time soon).

> Any idea why swapping didn't pan out for Tesla?

~~Two~~ Three things:

1. California changed the rules shortly after Tesla demonstrated their swap station, which practically eliminated the tax credit for battery swap (at the behest of lobbyists for Toyota, who were backing Hydrogen Fuel Cell technology). Specifically, the credit would be prorated by the percent of “fast refueling” sessions a car did, so EVs primarily charged at home received almost nothing while HFCV got the full credit. Building swap capability adds complexity to the car (think about all the fluid connections), which isn’t worth it without credits.

2. It was also around this time that a Model S ran over an anvil (or something) which punctured the pack and started a fire. In response, Tesla added an aluminum battery shield, which further complexifies swapping and was probably the final nail in the coffin.

3. The logistics of storing your very expensive battery (so you could get it back later) basically make the system unworkable. When the Tesla swap station at Harris Ranch (you can still see the former building, next to Harris BBQ, which currently houses the restrooms) was operational, you had to make a reservation some hours in advance so that Tesla could have a pack ready and be ready to take your pack to/from storage.

3a. Gresham’s Law. Without eventually returning the pack to the original owner, there is an adverse selection problem: people with very weak packs will gladly roll the dice on a swap, but those with brand new packs are reluctant. So the average quality of packs in the swap network will quickly decline creating a death spiral.

3b. You could probably fix 3a by leasing the battery (or selling battery-as-a-service) but car buyers mostly don’t like that, especially back in 2013.

In addition to all of that, it just doesn't outcompete recharging in the end.

Even if the swap station got to where it was hoped (no reservation needed, automated, drive in, swap, drive out), you'd have a choice between a ~5 minute stop at a swap station, or a ~10-20 minute stop at a charging station. The swap station is always going to be more expensive since it's inherently more complicated, so you're spending more to save a few minutes. And when you stop at the swap station you can go answer the call of nature and grab a snack while you wait. If you want to do either of those anyway, then visiting the swap station means you'll do the swap, then go do those other things, and probably not save any time at all.

Charging time just isn't that much of an issue at this point. I've been driving a Tesla for a decade at this point, with thousands of miles of road trips around the eastern US, and I've never found myself wishing for battery swap infrastructure. Newer cars charge much faster than mine does, too.

I could potentially see value in a car with a smaller built-in battery for use around town, and an empty space for a larger battery, that you rent from swap stations for longer road trips. Of course, that doesn't work with anything on the road today.

Probably because the economics just don't make sense here. You'd have to have so many compatible cars on the road, driving all day with no opportunity to charge. I'm having a hard time imagining a place I've been to in North America where that'd seem logical.

> they are doing that in China

Are they actually doing that at scale?

A little out of date now but:

> As of June 2024, Nio had installed 2,432 power swap stations in China, including 804 along highways, representing the largest battery swapping network in the country. Nio aims to expand to 4,000 stations globally by 2025. By February 2025, Nio had 3,106 battery swap stations in China, with 964 located along highways. In January 2025 alone, Nio added 111 swap stations and provided 2,949,969 battery swap services, averaging 95,160 daily.

https://enertherm-engineering.com/chinas-battery-swap-revolu...

From the country that brought you mass wastage of bicycles, now we get battery swapping.

This is pretty much just a "gamble by deploying as quickly as possible making our system the standard if it catches on" type of investment.

> Reduced Upfront Costs: Battery swapping allows drivers to purchase EVs without bearing the full cost of the battery, often the most expensive component.

I also wonder if it's a scheme to get people through the door and then leech off them with a lifetime subscription.