Many flagship phones promise 7 years of security updates now. 3-4 years means the battery will only last for half that time, and heavy users (1 cycle per day) will hit that quota in under 2.75 years.

The battery doesn't cease functioning after 3-4 years. The benchmark says it should have 80% capacity.

It's also not really that expensive to have phone batteries replaced. Apple will do it for $120 including the battery for their flagship models that cost over $1000. Cheaper for lower end models.

I can't take any arguments seriously that claim these phones are becoming e-waste after 2.75 years. Battery replacement is a common process.

Importantly “last” means that it will have at least 80% battery capacity left.

Then the law should just make sure that there's a second source at least for the batteries, that technicians have free access to disassembly instructions, and that it can be done without undue effort or risk.

Requiring common tools or technical skills for replacing something that last 4 years is not a hassle to justify enshitiffying phones design as long as you're not vendor locked for such replacement, and a technician can do it in a reasonable amount of time, with reasonable tool and without the risk of degrading the functionality of the device doing so.