Curious about using HR bands as Polar oh1

Most of those devices are made for just being worn when exercising.
How’s the battery life when using sleep recording? Is it 1:1 in amount of hours, like it drains as much as an 8 hour workout would?
Can some of them be worn passively like any wearable or do you have to “record an activity”
I’ve seen the Polar Verity Sense has gyroscope and does steps when exercising.

It’d be fun to make a DIY Whoop-band.
I also have a galaxy watch 4 I could connect it to during the day, and just charge the watch and wear the band at night.
Any tips on a device that could do this?