Body Battery with 2 devices

I have a Forerunner 45 (for 6 months) and now have a Fenix 6 Pro. I wear the FR45 overnight & working day, and the Fenix for evening/weekend activities. Body Battery is only recorded for the time I'm wearing the FR45. The FR45 is my primary wearable, the Fenix is my primary training device. Is this normal?