The following four steps show how to remove the battery from a 44 mm Apple Watch Series 6.

Insert an opening pick between the battery and the Taptic Engine.

Use constant, steady pressure to slowly pry the battery up, separating it from the adhesive securing it to the mainboard.

Make sure you don't puncture or deform the battery, as it can catch fire and/or explode if damaged.

Don't try to remove the battery all the way yet. It is still connected to the watch assembly.