TIL as well

Technically a bank is a much larger shareholder (https://www.mazda.com/en/investors/stockinfo/situation/), but Mazda and Toyota have been collaborating for a long time with joint manufacturing (https://en.wikipedia.org/wiki/Mazda_Toyota_Manufacturing_USA) and technology sharing. Toyota has similar arrangements with other companies like Subaru and Suzuki.

Toyota also owns Daihatsu, which is a lesser known name in the US, but is a major maker of kei cars, which are huge in Japan and other parts of Asia.

They also own Denso, which is the second largest auto parts company.

And they partner with Subaru on some things, such as the Subaru BRZ and Toyota GR86, which are basically the same car with different badging.

TIL Mazda isn't a wholly owned subsidiary of Toyota. I thought it was, now I wonder where I got that from.

I have to imagine that even accounting for the variance in internal resistance over a large set of batteries in a demanding application like a car is probably a host of problems makes this unattractive from the outset.

It's quite likely that lower discharge rate requirements are a large part of what makes this system function. Batteries with different internal resistance can work reasonably well even in a naive series system at low discharge rates but absolutely will not work at high discharge rates.

I suppose this has a better chance to happen in city trucks than in cars. Delivery trucks are used more heavily, owners care more about efficiency, they are bigger and taller, so they can offer easier structural options to house swappable batteries. Also, swappable batteries could make charging very fast, if a sufficient stock of batteries is kept on a charging station.

Cars could follow, but it's significantly more involved in them. In most cases, the batteries are a relatively thin layer covering the entire floor space, or similar.

Re: 1, ignoring the complexities, is really interesting but depending on the effort to change our battery banks quickly makes renting a car more feasible.

And this highlights American traffic and sparseness.

- plug-in hybrids have 10-13 mile range which is great for running a few errands (this is only slightly more feasible than in a golf cart or ebikes) - also great for last mile connectivity for mass transit n users;

- the Nissan leaf 2012 had an 80 mile range - perfect for most daily commutes in a metro area

- modern electric vehicles have 200-300+ mile range, good for weekend getaways; esp with a charge at the destination

GM claims that this is exactly how their Ultium battery pack architecture works. It is made up of multiple modules each with their own BMS, and supposedly one module can be replaced without having to be a match in chemistry and degradation to the other modules.

I'm unsure if that will actually work so well in practice, where you still need to charge all the cells simultaneously when doing DC fast charging etc.

Also all of that extra architecture adds cost and complexity to each vehicle that rolls out the door, compared to a pack that just packs in a bunch of cells together with the necessary cooling etc. as one contiguous unit.

Given that EV battery packs in the real world are trending to last longer than the cars they come in, going with a simpler pack design and swapping in a refurbished pack if you experience a premature failure might be the more economical route.

I hadn’t thought about different sizes/weights but this does remind me of Nio’s battery swap network. Which I’ve always been fond of in principle. I think at some point in the future, when range isn’t such a competitive advantage in the EV space we’ll see a push towards standardization and something like this will likely occur. I’d guess something around the 1000 mile mark for an EV. Absurd, yes, but at that point no one will complain about range and that sort of implied density/efficiency also allows for a better towing experience (at least here in the states). If someone can get a 1000 miles of range, but only drives 100 miles at a time TCO drops immensely because tires/brakes last much longer at lower weights.

CATL announced a dual-power battery pack recently.

https://technode.com/2025/04/22/catl-says-its-next-gen-dual-...

I believe we have a new generation of supercapacitors in R&D stage. There were some experiments done in the last year that showed that some assumptions about what makes supercaps work so well turned out to be wrong. I can’t recall the details but it turns out the foamy structure of charcoal is not the optimal structure. So that should result in higher energy density per unit volume.

A few tradeoffs you might not be considering:

EV battery packs operate at voltages that are seriously hazardous. Consumers coming anywhere near those plugs is a non-starter, so even more bulk, weight, and complexity would need to be added to make the installation process foolproof.

Waterproofing is critical, the mechanism has to work flawlessly over insertion/removal cycles to keep a watertight seal.

Did you even read the article? It has nothing to do with producing EVs, they are using the old EV batteries to help power manufacturing facilities.

it's unrelated to the manufacturing of EVs. If any factory reaches a significant energy generation (usually this means from solar) it makes sense to look into a battery solution. It just happens to be Mazda's manufacturing plant.

Mazda as a company has a very good track record of adopting green production initiatives. For example, they were one of the first to switch to water based paint to reduce VOC emissions, and specifically formulating the paint to not require heat-drying to lower energy use.

Their current stance seems to be that PHEVs are better than EVs for the environment because it better matches the driving patterns of the typical customer and charging availability, and minimizes the weight of the vehicle and production of batteries, both of which are still contribute significantly to pollution.

At the cell level they don’t degrade linearly. First it’s slow then it’s fast and then it’s abrupt collapse. You probably have noticed that yourself with old devices. Some do not hold charge even for a minute.

With battery packs probably you can do some smart things to make the degradation curve look more linear, but again there is only so much you can do.

this is like picking up unfinished cigarette butts and making few finals puffs before burning your mouth.

worn-out batteries can swell and fail spectacularly, with fireworks

If you take car EV batteries and use them for stationary storage when past end-of-life, the fire risk becomes fairly substantial because EV batteries often have a little water ingress, physical damage etc.

It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.

Battery banks are worse than degraded raid arrays in some important respects. The bad cells tend to try to bring the rest of the pack with them. It’s one of the reasons people keep toying with partitioning cells and putting controllers onto individual cells or small groups of them.

Parting out two or three dead battery packs to cull the best of the survivors can improve things quite a bit. And as you say, on a stationary pack you can afford to overdo telemetry, cooling, and safety circuitry because it doesn’t have to move, let alone accelerate.

I don’t know what the half life is like for the reused cells though. Do the cells that lasted twice as long as their neighbors continue to outperform or do they revert to the mean over time? I could see either being true. The days when you accidentally produce cells that are several stddev better than your target quality should make cells that last longer, unless they’re sold to a leadfootted driver.

More often than not these bad cells can be removed, manufactured a new, and reinstalled. Not 100% but almost good as new.

Making your own cells is fun.

For Toyota, this is trivial and the energy storage these “left over” batteries provide, given a tinkering, is sufficient.

I saw that 787B at the Adelaide motorsport festival, MAN that thing makes an incredible noise!!!

It's almost like EV batteries don't last long...