Next time a consumer get stuck with a practically irreplaceable battery because it’s too expensive from a company, they will look at other companies selling equivalent products, AND how much they are charging for batteries.

No. Just look at the current phone market. The average consumer doesn't care enough about repairs down the road, or at least it doesn't affect their purchasing decisions, they are mostly driven by convenience and familiarity. If what you're saying was true, everyone would be buying fairphones.

I also imagine a business of spare parts because just having to give the right data, e.g. specifications like cell, module, pack, C-rate, E-rate, SOC, DOD, voltage, capacity, energy, cycle life, but also connectors and just size, will probably open up dedicated spare part vendors.

Those specs are already widely available for many phones and in fact you can buy aftermarket 3rd-party batteries for most of them. The problem is that battery replacements are painful, require specialized equipment (at least a hotplate, suction cup, spudger for most phones) and skills (not breaking the screen/glass back, unglueing the battery without exploding it, then carefully glueing everything back together etc). This is what the law should be addressing first; if it were easy to replace batteries (like a 1-minute job instead of 30-minute job), you would see a lot more DYI replacements and probably way longer lasting phones on average.