And even if true, it doesn't follow for me that "therefor, batteries must become more expensive in general, despite the current trend".
I think you're implying lock-in and extractive profits, rather than rising cost of manufacture. It's an argument for diversity of key industries, and that batteries might become such. I agree with that. But as an argument that (in parent the comment's words) "so, battery prices will skyrocket", it seems a bit thin to me.
battery prices are expected to "Plummet" not "Skyrocket": https://cleantechnica.com/2025/10/15/plummeting-battery-pric...
Batteries are not a differentiated product. They're basically completely defined by 3 numbers: capacity (in watt-hours), power delivery (watts), and weight. Once those are optimized (which is the process going on now), the chemistry, construction, and manufacturing of batteries is basically a solved problem. Any barriers to entry are purely in the technology and manufacturing. About 200 years of industrial history shows that these are not durable barriers to entry: eventually, technology and know-how diffuses, and knowledge of how to make even very complex machines becomes a commodity. (See eg: power looms, memory chips, hard disks, agriculture, TVs, automobiles, drones.)
Durable competitive advantages usually take the form of either a.) complex consumer interface, eg. with software or CPUs b.) network effects, eg. telecommunications, payment networks, software again, utilities or c.) regulations, eg. payment again, airplane manufacturing, healthcare, and shortly software. These are industries where factors outside the company in question ensure that there will only be one or at most a small set of companies in the market.
When you have a commodity product, the only route to extractive profits is to form a cartel and lobby governments or consumers to believe the cartel is in their interests, eg. with oil or diamonds. But this is a hard sell because the cartel is not in their interests. You can generally only fool people for a decade or two before they decide they've had enough and legislate your monopoly out of existence.
People tend to overindex on the software industry when it comes to "maximizing profits" because that has been the big story of the 2010s, ignoring that Big Tech very carefully implemented every play in the "build a monopoly" playbook to get there, and that millions of indie software developers actually do not make a very good living because their products are commodities.
But the rest stands. The barriers aren't that high. How soon it is diversified, depends on how much attention the other countries and companies are paying.