7 ms·

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 cou

by zhyder 1y ago

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 1y ago
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 1y ago
  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.
momoschili 1y ago
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 1y ago
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.
smileysteve 1y ago
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
- lstodd 1y ago
  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 1y ago
    Small 2-stroke engines tend to be worse for pollution emissions (NOx, particulates) despite generally good fuel efficiency.
    - lstodd 1y ago
      well, yes, I like the smell of 2T exhaust in the morning. still, even my yamaha majesty 250 of 1992 (4HC-edit) only ate 3.5L/100km despite hauling thrice the mass of that same ovetto.
      - olddustytrail 1y ago
        Of course you do. As long as someone else pays for cleaning up after you. There have always been leeches in the world.
stetrain 1y ago
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 1y ago
  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 1y ago
    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 1y ago
      Separate power factor circuits for each pack, I would think. With everything switching over to GaN now and bringing the prices down that should be doable.
    - coryrc 1y ago
      I would expect you could only do it with the onboard charger and only if it has one charger per module or the ability to connect the singular charger to each module.
rubyn00bie 1y ago
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.
- 542354234235 1y ago
  It feels like Neo is the opposite of where things should go. The great thing about EV is that every outlet is a refueling station. More EV charging for apartment buildings and parking lots feels like the answer. Those battery swap stations are insanely complex and expensive, and the complexity and added weight on the car are very significant. Unlike a gas station that just needs two nozzle types, or an EV charging port standard, having to standardize battery packs for everything from compacts to trucks would be a nightmare. Most people are not taking hundreds of mile road trips most of the time. Slow charging your car while it sits at home or at work or at the shop will work for 90% of cases. I could see the case for industrial or work vehicles, where keeping them running constantly is a legitimate need, but for personal vehicles that sit in driveways, parking lots, or garages 80% of every day, battery swaps feel like massive overkill.
omgwtfbyobbq 1y ago
CATL announced a dual-power battery pack recently. https://technode.com/2025/04/22/catl-says-its-next-gen-dual-power-ev-battery-will-give-930-miles-of-range/ https://technode.com/2025/04/22/catl-says-its-next-gen-dual-...
- Dylan16807 1y ago
  Clarification, that announcement is for a new version and they're already selling packs with mixed battery chemistries.
hinkley 1y ago
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.
TGower 1y ago
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 1y ago
  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 https://youtu.be/Oj6LaYFall4); I think any battery swapping only makes sense for batteries you rent rather than own.
  - appointment 1y ago
    What does "imagined" mean? Nio has been doing automatic battery swaps on a mass scale for years.
- 542354234235 1y ago
  Also, you lose the ability to mold your battery along the bottom of the car, using dead space and keeping the center of gravity low. Gas tanks aren't even boxes, they are molded to fit around other parts with no dead space. So, add that space efficiency loss to all the additional space needed for access panels, installation foolproofing, additional waterproofing, etc.

by zhyder 1y ago

bri3d 1y ago

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 1y ago
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.

momoschili 1y ago

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 1y ago

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.

smileysteve 1y ago

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

lstodd 1y ago
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 1y ago
  Small 2-stroke engines tend to be worse for pollution emissions (NOx, particulates) despite generally good fuel efficiency.
  - lstodd 1y ago
    well, yes, I like the smell of 2T exhaust in the morning. still, even my yamaha majesty 250 of 1992 (4HC-edit) only ate 3.5L/100km despite hauling thrice the mass of that same ovetto.
    - olddustytrail 1y ago
      Of course you do. As long as someone else pays for cleaning up after you. There have always been leeches in the world.

stetrain 1y ago

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 1y ago
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 1y ago
  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 1y ago
    Separate power factor circuits for each pack, I would think. With everything switching over to GaN now and bringing the prices down that should be doable.
  - coryrc 1y ago
    I would expect you could only do it with the onboard charger and only if it has one charger per module or the ability to connect the singular charger to each module.

rubyn00bie 1y ago

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.

542354234235 1y ago
It feels like Neo is the opposite of where things should go. The great thing about EV is that every outlet is a refueling station. More EV charging for apartment buildings and parking lots feels like the answer. Those battery swap stations are insanely complex and expensive, and the complexity and added weight on the car are very significant. Unlike a gas station that just needs two nozzle types, or an EV charging port standard, having to standardize battery packs for everything from compacts to trucks would be a nightmare. Most people are not taking hundreds of mile road trips most of the time. Slow charging your car while it sits at home or at work or at the shop will work for 90% of cases. I could see the case for industrial or work vehicles, where keeping them running constantly is a legitimate need, but for personal vehicles that sit in driveways, parking lots, or garages 80% of every day, battery swaps feel like massive overkill.

omgwtfbyobbq 1y ago

CATL announced a dual-power battery pack recently. https://technode.com/2025/04/22/catl-says-its-next-gen-dual-power-ev-battery-will-give-930-miles-of-range/ https://technode.com/2025/04/22/catl-says-its-next-gen-dual-...

Dylan16807 1y ago
Clarification, that announcement is for a new version and they're already selling packs with mixed battery chemistries.

hinkley 1y ago

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.

TGower 1y ago

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 1y ago
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 https://youtu.be/Oj6LaYFall4); I think any battery swapping only makes sense for batteries you rent rather than own.
- appointment 1y ago
  What does "imagined" mean? Nio has been doing automatic battery swaps on a mass scale for years.
542354234235 1y ago
Also, you lose the ability to mold your battery along the bottom of the car, using dead space and keeping the center of gravity low. Gas tanks aren't even boxes, they are molded to fit around other parts with no dead space. So, add that space efficiency loss to all the additional space needed for access panels, installation foolproofing, additional waterproofing, etc.