I don't see this BYD alliance with NIO and XPeng at all. Here is the tweet showing that battery installation effort of CATL and BYD from Q1
Notice how over 95% of BYD's EV batteries were installed on BYD vehicles?
Whereas for CATL, about 20% of its capacities were installed on Tesla and the rest is kind of even divided among many automakers. CALB is mostly installed on GAC and Xpeng, but also has a lot larger customer base.
This just confirms Taylor Ogan's comment that everyone is knocking on BYD's door for its blade battery technology, but it's too busy building its own vehicles with it. You can see why BYD is building so many battery factories at the same time. The current production level can barely cover BYD's own expanding EV production. Also IIRC, NIO is look for semi-solid state battery for its cars. That's something BYD does not currently produce. So, I think BYD will be very selective about its alliances. It has picked one with Toyota. I think it will use that Toyota partnership to access more international markets. As of now, Toyota is probably complaining BYD is too busy building EVs and batteries for itself and not for their JV. I also see BYD partnering up with Apple or another American company for greater presence in US market. It would be much harder for US government to block BYD produced vehicles if they are under a JV with a well known American brand.
I do see cooperation between BYD and NIO/XPeng when it comes to charging station and charging standard.
This makes a lot of sense to me. They can only export more if the international market has charging stations that can charge their cars. Tesla is notorious for having its own proprietary super chargers that don't work with other EVs.