Hi,
I use the 945 as a running watch, the vivosmart 4 as a daily/nightly activity tracker. Both watches have Body Battery support, and the vivosmart 4 does a good job at it, but when I put on the 945 i get huge spikes/drops in my BB-graph - it seems the 945 has a completely different idea of my BB value, and depending on which watch I wear i will get completely contradicting data.
Example:
Today my BB topped up to 100% over night, and was sitting at 100% since I woke up, all using vivosmart 4. Then I put on the 945 to test some settings, and the BB dropped down to almost zero. Put back the vivosmart and it popped up to close to 100% again. On the "My Day" page in CIQ i see Body Battery +530/-468 currently, just from this back and forth between the watches. I have enabled True Up to sync activity tracking stuff between watches, but i do not think body battery is part of True Up, from what I read.