Starting with the removal of the battery, which appears to be made of 3 cells.

Disconnect the battery by pulling the cable out of the motherboard

The battery is held in with a single PH0 screw. Once removed, it can be pulled out.

Opening up the battery does, indeed, affirm it is made of 3 cells, as wekk as a controller.

The battery appears to have an internal sensor for temperature, to protect against it exploding in unsafe environments.