[Quoth]

Only if you think $10 to $15 is pricey. Some Kindles such as DX and KK3 are easy to open, others harder and some are almost impossible.

The Oasis might be almost impossible. There are 5 or 6 sorts of Paperwhite. Some might be popped open.

Sadly the Lithium cells also age with time and temperature, not just notionally complete cycles which can be 100 to 1000 depending on quality and temperature.
My PRS350 must be close to 12 years old and still reasonable life. I've had to replace KK3/K3 and DXG batteries (really cells) about 9 years old and phone batteries only 5 years old.

Phones batteries can have the worst life due to needing charged far more often.