like this law isn't about users causally replacing batteries like on very old phones
but about an repair shop easily and without risk of breaking your phone being able to replace it without only holding on your phone for idk. 10 minutes
So that you can just drop by (once they have the replacement parts) wait a moment and have a new battery.
This means in the worst case something like needing to a add a bit of additional seal/wax/glue or similar to improve sealing is very much fully viable (Id the sealing agent is generally buy able.)
It just is something you have to design in from the get to go. And it's easier to not do so at all. And maybe if you obsess if your phone is 1/10mm smaller or not that gets in your way too. And not doing so is more profitable as people will buy successor products more likely, even if just very slightly more likely.
But in general? That really isn't the problem.
Also even if it where the problem. What is better? Having a less waterproof phone, but not needing to buy a new one for another one or two years or having to buy one now?
iff
- it's generally commercially available
- and re-applicable after replacement with just generic tools
- and removing the battery doesn't risk breaking your phone due to physical strong binding glue being used as sealant etc.
As a dump example you can design the phone as a sealed unit with the battery department being "outside" the seal. Then have the battery also sealed and apply a bit of "sealant" (wax?, glue?) on the electrical contacts braking the seal on both sides. As the battery and battery compartment back have to only be waterproof and not "rigid" this probably fits "just fine" into most phones (except the most over the top slim ones).
Which is probably more the actual problem. Thinks like phone makers over-obsessing with making phones slimmer on a sub 1mm standard ... and then people anyway putting "thick" cases on the phone to protect it...