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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 applic

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.

benoliver999 9mo ago
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
- magicalhippo 9mo ago
  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 https://www.nature.com/articles/s41560-024-01675-8 Dynamic cycling enhances battery lifetime (open access)
  - LordDragonfang 9mo ago
    Huh, unexpected is right. Bursts of heavy usage being better for longevity than steady usage goes against pretty much all conventional engineering wisdom.
    - abdullahkhalids 9mo ago
      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.
      - magicalhippo 9mo ago
        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.
1980phipsi 9mo ago
Any idea why swapping didn't pan out for Tesla? My understanding is they are doing that in China.
- barbazoo 9mo ago
  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?
  - fartfeatures 9mo ago
    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-revolution-is-this-the-future-of-evs/ https://enertherm-engineering.com/chinas-battery-swap-revolu...
    - fennecbutt 9mo ago
      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.
      - barbazoo 9mo ago
        > 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.

benoliver999 9mo ago

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

magicalhippo 9mo ago
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 https://www.nature.com/articles/s41560-024-01675-8 Dynamic cycling enhances battery lifetime (open access)
- LordDragonfang 9mo ago
  Huh, unexpected is right. Bursts of heavy usage being better for longevity than steady usage goes against pretty much all conventional engineering wisdom.
  - abdullahkhalids 9mo ago
    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.
    - magicalhippo 9mo ago
      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.

1980phipsi 9mo ago

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

barbazoo 9mo ago
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?
- fartfeatures 9mo ago
  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-revolution-is-this-the-future-of-evs/ https://enertherm-engineering.com/chinas-battery-swap-revolu...
  - fennecbutt 9mo ago
    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.
    - barbazoo 9mo ago
      > 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.