How to open Oasis 3 to change battery?

I would like to know how to open the device to change the battery. At the moment it is not necessary but because the battery runtime is about the same on my 6 month old Oasis 3 as on my 6 year old (heavily used) Paperwhite i bet that i will have to change the battery after ~3 years.

Don´t get me wrong. I love my Oasis. Size, buttons to flip pages, automatic orientation rotation and case shape (which makes it extremely comfortable to hold). But the battery size is a joke. One day of heavy reading and the battery is down to 10%. If i could easily open the case i would try to fit a bigger battery.

I did some modding with my old Paperwhite years ago. And also changed the Battery after a few years. Even added a Qi receiver to charge it wireless.

Probably will try to open my Oasis in the future when the battery gets weaker. At the moment the battery is still to good to risc damaging the Oasis by opening the case.

Here two pics of my old Paperwhite