So I've been critical in the past of the efforts going on in this space, and it seems not too much has changed in the meantime.
First of all, I completely agree that a replacement main battery should be the next obvious step forward to extending the lifespan of these vehicles. Compared to extender batteries, this is much easier to install, does not encroach on usable space in the car and is just the more obvious choice.
However, main battery replacements run into two really big and expensive issues rightaway: homologation and safety. Any new battery will become a direct drivetrain modification, and that is something that in most countries - especially those with a large contingent of Leafs - requires Nissan to agree that the product is safe to use in their car. If it's not homologated, you're driving an uninsurable car. This is not a scalable solution and even if just a tiny proportion of batteries causes issues down the line - that's more harm being done to EVs, sustainability and Leaf owners than good. Worst case, Nissan or national regulators will actively kill the entire aftermarket battery industry. This is something to avoid at all costs.
Safety is also a serious issue; the main drive battery is mounted in the weather and in close proximity to the ground, meaning it needs to have protection against piercing debris, an internal structure that is stiff enough to avoid cells touching in case of impact, etc. This requires quite some simulation and paperwork to be accepted. Even if you reuse the old battery shells.
And then, let's consider why we're doing this in the first place. The old Nissan batteries - hell, the new ones too - are defective by design. They do not have thermal management and have to some extent underdesigned battery management. Also, older batteries are way too small to be practical as an everyday car. If you're designing a replacement, this has to fix all of these issues. We've seen Renovables del Sur and the Ukrainian guy make replacement Leaf batteries - but with a very narrow focus on just packing as much capacity into the shell as possible - not solving the actual reason we're replacing them in the first place! Moreover, the original BMS and shell are reused without regard to safety and compatibility, which is understandable from a cost and development speed perspective, but an accident waiting to happen if you have experience in the field. To be clear, MUXSAN adheres to the design process known as 'fail fast' - try things out, weed out the failures, learn from them and get to an optimal design faster as a result. But that's not the whole process; you do still need to do proper design. Most efforts to add battery capacity to the Leaf stop considering their design requirements at 'needs more batteries'. Then continues with 'needs to be cheap' and engineers from there.
Because let's face it, the products we design today should and will be used for the life of the car. I see no reason why you can't drive a Leaf for another 10-15 years at least. So these battery replacements should continue to operate to not just today's requirements, but also looking forward to future requirements. People are not going to be happy with a non-thermally managed battery that fails in another 5 years. People are not going to be happy when they're limited to 30ish kW fast charging in 2025. People are not going to be happy having to physically disassemble the pack to troubleshoot it. You need to design for longevity, which means both overdesigning the internal systems to last longer than the original batteries and overdesigning the battery specs to cope with future demands like 150kW+ fast charging and operation in hotter climates.
Oh, and it also needs to be cheap enough to make sense to current Leaf owners. That really is where you start getting into issues. This year, MUXSAN is hoping to produce at least 5MWh worth of battery packs - enough for about 200 Leaf extender packs. At that kind of battery volume, we're struggling - with a cost-optimized design with less stringent requirements than a main battery replacement - to get below $300/kWh. Just straight development costs - the materials, prototyping, etc. needed to get this working - are about $150k for this product and it will take 1000 extenders before we break even on R&D.
Say you want to properly design a Leaf replacement pack. Homologation is going to require not just any engineering, it's going to require Nissan to take notice and be willing to lend their engineers from Japan to us to do certification. That's hundreds of thousands of dollars in external consulting. They will not allow for large parts of the software to be open source for fear of IP leakage. Then you're going to require certification in at least a few large markets to be able to get to the sales volume you need to offset costs. It's about $25-50k to fully certify our extender batteries in the Netherlands, so let's say it is a similar amount per country - that's another few hundreds of thousands of dollars in certification. Altogether, it's easy to spend a million dollars just on paperwork and external auditing/engineering.
Say you've passed and you can capture a few percent of the used Leaf market - that's at best 5000-10 000 batteries you can sell. What kind of battery? People are going to want something between 40-60kWh, right? Say at this volume you can push sale price to $250/kWh. That's $10k-15k for a battery. Are people going to pay that for a $5k car? Sure, we have plenty of customers willing to spend that kind of money on their old Leaf, but does that customer base scale far enough?
Oh and all of this needs to be done pronto. People are not going to wait another 5 years for this to be done. Half your customer base will be on the scrapyard by then. Again; it's not even an engineering issue. Engineering a battery like this is not that hard. Setting up production, scaling and bankrolling all of this effort in short order is. Making an EV battery is not quite as hard as making an entire EV, but it comes pretty close!
This is a Very Hard Problem. You've got to move very quickly in a very capital-intensive market, hoping to capture a waning customer base, trying to sell a $10k+ product to thousands of people in dozens of countries. If you do it wrong, regulators are going to swoop in and kill you. For good reason.
And this is why we're still prioritizing the extender battery solution. Obviously we'd like to develop a replacement battery. We might very well do that this year, just to try it out. But I don't expect this to go very far until either we or other companies become large enough and rich enough to bankroll, on relatively short order, a surprisingly/depressingly large undertaking like this. Hey, maybe the real way forward is trying to grow MUXSAN so fast that we're able to be bought out by a large industry player and use their resources to make this happen. It really takes something like that to make this work.
And of course I'm writing this very much from my and my company's perspective, but I think true competition in the field will only work to further legitimize the industry and bring the prospect of third party battery replacements closer. As critical as I am of the efforts so far, from a systems perspective I don't want these companies to stop. The solution here is not to try, fail, then stop. I'm not saying failure is bad, even. But learn from it and create a better product next time.