I disagree. I'm still using hardware that I bought at the turn of the century (a wireless mouse and an MP3 player) because they are powered by rechargeable AAA cells. If they used a built-in battery, I would have had to replace the battery, which is much more complex than changing a AAA cell.

I have three recent electronic devices that I would like to keep using but cannot, as their battery has reached end of life, replacements are hard to find, and changing the battery involves performing surgery on the device that I'm not confident I can do safely.