Changing a part number has an enormous cascade effect. Stopping production of the old part and build out has to be managed. The ramp up for capacity of the new part has to be managed even if it is just adopting an existing part (do the existing machines have headroom for the additional capacity?). It has to be synchronized with the request of the vehicle plant building the cars to minimize parts that will be scrapped when the vehicle plant changes over.
Now, say you are through all that. You've already built 2 model years with an old battery and are now switching to a new one. The service parts warehouses will still need to stock both versions. The companies that built the old battery will still need the capability to build the old battery as a service part. The ECU has to be able to make use of that new battery's better capabilities. Now you have another ECU part number (or at least manage the software that is flashed to the ECU). All the repair manuals, etc all need to address the change. Does that new battery and new ECU impact fuel efficiency or emission ratings? That testing needs to be done as well along with filing with the relevant government agencies that control those things.
Unless there is a drastic safety or reliability benefit to the customer, it makes sense to keep building what they are already building in most cases.
And Apple (foxconn, etc) is literally building the SE, 12, 13, and 14 all at the same time. If you buy an iphone 12 today, it was likely built within the last 3-6 months... not back in 2020 when that model launched. Everyone uses JIT manufacturing these days.
Thanks for the detailed reply.
But what you said here kind of validated my argument. The problem is exactly that they keep too many SKUs even for similar products that should be simplified into fewer, interchangeable parts. An example is the A25A-FXS based hybrid systems.
With the new Crown Crossover they introduced a "small 350h" system with the 88kW 3NM motor, same as the previous 300h system. So now the 350h system has two different hybrid transaxles (P710 and P810).
This new "small 350h" system uses a 230.4V 5Ah NiMH battery that is shared with the "small 500h" system used on the Crown hybrid max. But the hybrid max has a higher amp rating (250A) and bigger cooling system. The Highlander and Sienna hybrids use a 288V 6.5Ah NiMH battery. But then on the NX350h, it's a 259V 4.3Ah Li-ion battery. On the RX350h it's another SKU, a 259V 5Ah NiMH battery. On the RX500h it's again a new part not shared with the Crown hybrid max, a 288V 5Ah NiMH battery.
If we now count the 300h system, we also have a 259V 6.5Ah NiMH (Camry hybrid XLE), a 259V 4.0Ah Li-ion (Camry hybrid LE), a 245V 6.5Ah NiMH (ES300h, RAV4 hybrid) and a 252V 3.7Ah Li-ion (Harrier/Venza).
So for just two powertrains, 300h and 350h, they have to keep 8 different battery SKUs, and if we include 500h, 10 SKUs. It makes zero sense the battery from the RAV4 hybrid is not interchangebale with a Harrier, NX, ES, or Camry. If I get any part for an A25A-FXS engine, I could use it to fix any of the models above, but not for the battery. It makes zero sense the Camry and ES300h use 3 different battery SKUs when they roll off the same line.
We also see this lack of interchangeability in the bZ4X. The industry has been using standardized form factors since 2018. Yet Toyota decides to use two completely different form factors for the Panasonic-equipped and CATL-equipped models.
