For the past ticwatch models these particular batteries were used : (for 1st gen pro ***LSSP452929SF***) also noticed that alternative replacement batteries went by ***SP452929SF***.
For the ticwatch 2 the ***SP372728SE*** was used.
Sadly could not find what exact battery was used in the 3 pro but there is a slight chance of interchangeability - unfortunately most of the third party/replacement batteries for the ticwatches are in the 400mah range rather than the 577mah of the 3pro.