Skip to content(if available)orjump to list(if available)

Toyota is recycling old EV batteries to help power Mazda's production line

pornel

Those who TL;DRd - it's for the factory, not the cars!

Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.

hinkley

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.

arghwhat

A degraded battery bank does not mean a bank with outright "bad" cells. The cells will probably be way more off than they used to be, but there can still be plenty of effective capacity in the bank. Heck, if space isn't an issue, it's productive as long as it isn't self-discharging too fast.

You can still have a working battery even with some "bad" (i.e., way out of spec) cells, depending on the BMS. All the thresholds are configurable, just that a regular EV setup would lean towards safety.

blkhawk

plus if you aren't making your packs unrepairable on purpose with foamed construction (like Tesla). you can par out modules in the packs into new configurations somewhat easily for the amount of work needed.

Saris

There's usually a pretty big gap in time between 'worn' at say 70-80% of original capacity, and a pack that has actual failed cells in it too.

snickerbockers

>The bad cells tend to try to bring the rest of the pack with them.

This is true (and in some cases potentially dangerous) when you have a several cells of varying voltages in parallel but it's fairly trivial (by EE standards at least) to overcome this with something similar to a charge pump.

null

[deleted]

CyberDildonics

You are talking about cells going bad and they are talking about cells that have less capacity from being cycled, not the same thing at all.

whatever1

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.

jama211

There’s quite a lot you can do when you can isolate and deactivate individual cells, big battery packs like this really do not fall off a cliff in the same way you’re describing.

carlhjerpe

How do you achieve this with cells in series? Do you kill an entire row and put it on "maintenance voltage"? I know how balance charging RC batteries work but they're smaller scale and "single row".

Also in RC car world it's generally preferred to have one cell per voltage step, I've had way more dual-cell(per series) packs fail than single ones. Though my experience is only 6s/~22v but it's "the same shit on a bigger scale" as far as I can comprehend.

elevaet

Sudden failure in a big battery like these is usually due to a single cell failing, which can usually be replaced and then the battery pack is back to the 70% capacity or whatever. Probably in this context of scale it's worth doing the work of replacing bad cells.

bluSCALE4

You do realize these batteries you're referring to resale at a decent price because, for the most part, they still function really well, just not in its existing capacity.

reactordev

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.

Dylan16807

Your own cells? Like you put together a lasagna of metal sheets and chemical goops and roll it up?

reactordev

Nah, you can buy 18650 cells, nickel strips, a spot welder, and make a BMS. Build your own battery pack.

londons_explore

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.

Cthulhu_

I've seen a video on the youtube where a battery recycling company does this; they leave the car battery packs in their original housing, which I presume is water resistant enough. Each unit is also connected to a controller, which I also presume monitors battery health, temperature (assuming temp sensors on car battery packs), voltage, etc. If a unit is dying they can safely dispose of it, else, the units were out in the open and with several meters in between, meaning any fire would be unlikely to spread to something else and there's plenty of access opportunities.

Very space inefficient though, but there's more than enough of that in the US.

carlhjerpe

How much distance does one pack realistically need to not cascade? Honestly I can't imagine any more than half a meter since air is an extremely good insulator. Just make sure the fire can't crawl across though cable insulation?

I've personally set RC lipo on fire with the wood-nail-hammer technique and while the fire out of the pack is intense I can't imagine it igniting another pack.

hinkley

Precautionary principle. There’s not good ways to extinguish these fires once they start. So you kinda have to let them go. Maybe you could use some sort of deluge system or aggressive liquid cooling on the surrounding cells however. Overbuilding the delivery system but then running the pumps at their most efficient cfm except when the smoke alarms go off.

lazide

Eh, the math is probably pretty different with massive quantities of packs in racks.

I’m imaging every firefighter I’ve ever known suddenly having the hair stand up on the back of their necks.

byw

Maybe they can also make the boxes out of concrete for a lot cheaper?

slt2021

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

Cthulhu_

Except that the cigarrette is only 30% smoked and still perfectly fine to smoke for a while longer (if you insist on an analogy).

Car battery packs are really good; even the oldest Teslas are only now getting to less than 80% capacity. They are designed not to swell/fail if they're worn, else there would be a lot more car fires.

bityard

I think you may be confusing worn-out batteries with damaged batteries, these two subclasses do not have the same properties

hinkley

Car power packs are batteries in the other sense of the word. They can be disassembled and culled. So what matters is the health of the best 1/kth cells in the array not the overall array health.

robin_reala

If you’re ever in Hiroshima I can recommend a trip to the Mazda museum (Cosmo! 787B!), which includes a factory visit across a raised gantry. It’s free, but you need to book in advance: https://www.mazda.com/en/experience/museum/

jama211

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

robin_reala

Also an iconic paint job. Mazda UK did a special edition MX-5 with a turbo and that paint to celebrate the Le Mans win: https://www.pistonheads.com/news/ph-features-heroes/ph-heroe...

zhyder

Neat idea to mix batteries of different age and chemistries. I've wondered why EVs couldn't do that too with some power electronics and SW. If an EV battery could have multiple such modules, it'd:

1) Make it easier to carry a cheaper lighter less-natural-resources-consuming battery most of the time. Go to some "gas station" to rent and add more modules when taking a road trip

2) Make it cheaper to replace the 1 module used a lot at its EOL, thereby making EVs last longer and be viable as cheap used cars even past 10 years like ICE cars are

3) Allow easier upgrades as chemistry improves: solid-state, sodium ion, etc.

Modules could be electrically tested for fit. I'd think the fit range would be quite wide (e.g. if one supported lower max discharge rates than another) given the headroom we have with EVs' power these days: they have far-more-than-needed power (which mostly comes for free with EV range).

The tradeoff is that they'd need to be built to be modular with some standardization on module dimensions (maybe we'll have "ZZ" size like we have AA, C, etc today), and would take a tad more volume in the vehicle (though the limiting factor is weight rather than volume). Easily worthwhile over the current model with a huge monolithic pack.

bri3d

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.

lstodd

exactly.

state-of-charge / depth-of-discharge vs lifetime accumulated "discharge stress" so to say also matters a lot.

batteries aren't simple, even lifepo4 ones.

TGower

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.

zhyder

Great points. Re safety, I wasn't imagining the consumer doing it themselves but some robot like ones imagined for whole-battery swapping (e.g. https://youtu.be/Oj6LaYFall4); I think any battery swapping only makes sense for batteries you rent rather than own.

momoschili

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.

nine_k

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.

omgwtfbyobbq

CATL announced a dual-power battery pack recently.

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

Dylan16807

Clarification, that announcement is for a new version and they're already selling packs with mixed battery chemistries.

stetrain

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.

hinkley

You shouldn’t need to charge them all at the same rate. Put in some cells that charge slower, fast charge the rest and continue charging the slower cells until unplugged. Consider for instance fast charging the array to 70% instead of 80%, where 1/3 of the cells are charged to 50% and the rest to 80%.

stetrain

When all of your cells are connected in a pack of 400-800V connected to a DC fast charger, how do you stop charging the fast cells and continue charging the slower cells?

hinkley

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.

smileysteve

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

toast0

PHEVs were quoting 20+ miles on electric last decade, I think 25-35 is common now?

Actual distance depends on elevation changes and speed/driving, but 15-20 is quite acheivable, as long as you don't make it to highway speeds. And if you go a bit farther and use a splash of gas, no big deal, that's why it has a tank.

Uvix

25-35 is common, and some like the Prius PHEV can do 45.

hinkley

I’ve done the math a couple of times and IIRC if we can get the charge density per kilo to about twice what lithium ion can do, you hit a point where a deposit battery that’s around 20 kilos has enough range extension to start being worth doing. That’s the weight of a large bag of kitty litter or a commercial bag or rice. Put a good ergo handle on it and most people should be able to lift a few of them consecutively.

But until one unit is worth about 8 miles of extended range, there would be no point. 3@25 or 30 miles might make it worth the trouble for a road trip, or camping.

lstodd

actually if you can get a late-1990-ish 90-100cc 2T japanese scooter like Honda Lead 90 or Suzuki Address 100, or even later Yamaha Neos / MBK Ovetto 100cc of 2005-ish vintage this whole discussion about ranges and fuel consumptions becomes pointless.

because those have had fuel consumption of like 2-3L per 100km. with fuel tanks of about 6L you had all the range for errands you could possibly need.

and they were capable of moving two persons around _and_ moving a ton of grocery, or something like an ironing board.

hell, in 2000s we were doing 700km trips on them.

stetrain

Small 2-stroke engines tend to be worse for pollution emissions (NOx, particulates) despite generally good fuel efficiency.

bluGill

had to check: toyota owns 5% of mazda which makes them the largest shareholder.

redwall_hp

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.

kenhwang

Toyota owns a de facto controlling stake in Subaru (~20%).

Due to typical Japanese corporation by-laws, it only takes 33% share ownership for uncontested control of a corporation, and >50% of 33% means they'll never lose a vote for simple majority matters, which is basically everything except selling or dissolving the company.

The 20% threshold is for a guaranteed seat on the board, which lets them put issues up for a vote.

omega3

> Due to typical Japanese corporation by-laws, it only takes 33% share ownership for uncontested control of a corporation

It doesn’t make any sense.

hinkley

They also owned a chunk of Mitsubishi Aeroplane and IIRC invested in Mitsubishi’s 787 manufacturing division.

neogodless

re: Subaru

Perhaps more relevant, the Subaru Solterra and Toyota bZ4X (renamed bZ for 2026) are on a shared EV platform.

burkaman

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.

kenhwang

That's a trust account though, they're just holding shares on behalf of fund managers or individuals. They also generally don't vote.

So for all intents and purposes, Toyota is the largest singular voting shareholder.

wiredpancake

[flagged]

lupusreal

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

bityard

Related: Ford once had a 33.4% stake in Mazda and there was a bunch of cross-pollination between the two companies at that time. My 2002 Mazda Protege was loaded with various parts bearing the FoMoCo logo. And Mazda engines/chassis powered a bunch of Ford cars world-wide.

bluGill

Ownership changes over time. At one time ford was in control. Which is why I checked - what toyota is doing makes no sense until you see current situations, now there is an obvious expected return on investment (if it works out of course- if it does they will do this to their own factories, if not they will write it off and not lose much.)

throwawaymaths

TIL as well

themaninthedark

IIRC; Toyota started investing in Mazda to gain access to their engine technology.

https://en.wikipedia.org/wiki/Skyactiv

https://thedetroitbureau.com/2019/07/toyota-teaming-up-with-...

robofunk

What's interesting is that if the batteries are being sourced from JDM cars the batteries are probably relatively young due to the average age of Japanese cars being relatively low (8.7 years) and the amount of yearly mileage is also half for JDM cars when compared to the US. So if you tried the same in the US it may not be as viable.

wiredpancake

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

stanmancan

Turns out they're lasting much longer than expected: https://news.stanford.edu/stories/2024/12/existing-ev-batter...

wiredpancake

Nope. Why would Toyota even have an abundance of "old" EV batteries to begin with if they "lasted much longer than expected".

I have a Toyota Landcruiser from 1990.

skhameneh

This seems very bizarre given Mazda is probably the least (of all "major" manufacturers) focused on EV and electric initiatives.

Mazda only had one EV, the MX-30 EV. Less than 600 of the MX-30 EV were sold in the US during its production. It was a complete flop right out of production. Mazda leadership has been notorious for pushing rotary engines and shifting further away from EV initiatives.

kenhwang

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.

yabones

Mazda punches way above their weight when it comes to "moonshot" innovation over and over again. Few of them really "succeed" commercially (Rotary engine, miller-cycle engine, HCCI) but I respect them for constantly pushing the technology forward.

* https://en.wikipedia.org/wiki/Mazda_Wankel_engine

* https://en.wikipedia.org/wiki/Miller_cycle

* https://en.wikipedia.org/wiki/Skyactiv#Skyactiv-X

* https://en.wikipedia.org/wiki/Homogeneous_charge_compression...

skhameneh

In theory, that seems sound. In practice, there is very little information on efficiency details for vehicles like the CX-90 PHEV. At first glance, it seems other manufacturers are outperforming Mazda's PHEVs with standard hybrids.

There are so many questions this (the battery storage) raises regarding ROI and alternatives. I think it's great they're trying something, but I can't help but wonder if this will be another failed attempt on their track record.

wallaBBB

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.

skhameneh

The batteries are sourced from manufactured EVs. This is a later stage of the battery lifecycle that began with manufacturing of an EV.

momoschili

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.

Loudergood

This is very bizarre because that's exactly what GP was pointing out.

null

[deleted]

momoschili

seemed like they were pointing out that Mazda EV offerings are bad and that they don't worry about EV initiatives. That doesn't have much to do with studying how to put older batteries to use - EVs can be bad for many reasons.

To me it seems perfectly reasonable to try to find a way to leverage depleted EV batteries for a factory - whether or not it's producing EVs or not.