Body Battery on my 6x Pro is uncanny how accurate it is.

Fully agree on this. Body battery is very accurate for me too.

(If only calories count worked as it should)

It seems pretty good to me, too. I'm not sure If I'd say it's been "spot on", but it's been close enough to at least give me a good idea of where I'm at.

For example, if I start falling asleep at my desk at work, sometimes I'll look at my stats and see if I can figure out why, and see that my body battery is at like 15% (which I'll usually, then, look at my sleep metrics to figure out why that happened). Likewise, it's nice to see my body battery being over 90% before I start a strenuous activity.

Occasionally it's seemed a bit off. Where I'll be fighting to stay awake and barely have energy, but it says 80%... or vice versa. But I've found that that majority of the time, it's pretty good. And I like having this metric. It sort of motivates you to get more rest so you can "recharge".

Had a hangover recently and my fenix pointed out a flatline as a result of the poor sleep . Works very good for me too. Useful feature.

Yeah, that'll do it 

I've noticed that, too. It's actually pretty amazing how well it seems to figure your sleep quality into the body battery calculation. Sometimes an alcohol-related poor sleep-quality night has resulted in my body battery dropping instead of going up overnight - which is probably accurate considering I felt much worse the next morning than I did the night before 

If you think about it, it's seriously impressive for a watch to be able to figure that out, considering there's no way it knew I was drinking the night before.

With all the problems we've had with sync issues from Garmin Connect the past week.  My battery is getting low 

Maybe it has a secret camera recording those beers and wines

I do wonder how much more info it can give compared to the stress widget (heart rate variability) and sleep widget that I already have on my Fenix 5X. I can se how many hours I have sleept, I can also see how the sleep quality was in a way with heart rate variability during the night, with yellow staples high stress it aint so good, less recovery during the night. I can se my training load, if its to little or to much training and also heart rate variability during the day and after a training. I think they have made it easier to understand with the body battery function. But I can not pay almost 1000 dollar to get that function ha ha. Anyway, drinking can have a hugh impact on heart rate variability and sleep quality and recovery during the night www.firstbeat.com/.../

It doesn't seem to be providing "more info" exactly. I think it's just a simplified calculation that considers all of those factors, and spits out a number from 1-100 so you can quickly see how you're doing.

Otherwise, yes I think you can look at your sleep, stress, etc, and sorta figure it out on your own, too. It's just nice to have the watch do all that work for me and make it super simple to understand.

Yes I think You are correct. For them who wants to read more about heart rate variability and body resources (body battery) can read this excellent information. It shows the stress widget 24/7 www.firstbeat.com/.../