I just finished the Pixel 3 battery replacement. This guide covers all the steps well. For re-attaching the back to the case I used the 1 mm width tape available from this size. The precut card was not available at the time I was ordering parts. I guessed on 1 mm but after using it, it seemed to work well. I cut long, straight lengths for the sides and top & bottom, and then filled each corner with a short piece placed diagonally. Seemed to hold ok.
Thank you for the excellent guide.
What thickness(es) of tape is/are required to complete the battery replacement process?