I have replaced my iPhone X's battery after 4 years for %12 of its sale price. I had to wait longer than expected because my phone was a first generation device of its model number (Apple does silent internal revisions of the same model over time), so they had to upgrade a power managenent firmware normally not covered by iOS updates. Also, they have changed my speaker free of charge because apparently it was defective or broken in a way I didn't know.
After three years, my phone is out of support, with battery health at 90%. Considering my phone is out of support starting this year, this is neither expensive, nor planned obsolescence.
I'll save and buy another iPhone (the latest and greatest) in a couple of years, and will use that one for a decade, too.
How this is gouging the customer?
I support replaceable batteries, that will be great, but current practice is not to make batteries so expensive that people prefer newer phones, on the contrary.