Body battery is a useless gimmick

Counterpoint: Body Battery is useful, if it's getting good data, and you understand the underlying model.

Body Battery is one thing: a rolling total of HRV stress. That's it.

• If your HRV stress is "at rest", Body Battery will recharge. 
• If your HRV stress is above rest, Body Battery will deplete, at a rate correlated to stress level.

HRV stress:

• requires proper watch fit for accurate data... garbage in, garbage out.
• Is a measure of allostatic load, the physical, not psychological wear and tear on your body.
• would be elevated after drinking or eating greasy food until your body processed it out.

More info on HRV: https://www.firstbeat.com/en/blog/beyond-heart-rate-heart-rate-variability/

Garmin's instructions on correctly wearing your watch: https://www8.garmin.com/manuals/webhelp/forerunner945/EN-US/GUID-F2E7E0A9-FB44-4297-BF4D-D0C31C400C45.html

I'm having a different view.

Body battery isn't complete - definitely it isn't useless.

I find myself resting w/o it rising, yet during sleep it will rise.

Also, I never had a scenario like yours while in a stressful action it is rising.

mine is working fine. ok i also had a short period of low body battery % but at this same time i had more stress HSV high measurements. even during mi sleep period it hardly load my body battery. I doupt at that moment obout the item.

But now, less stress after medical intervention i was waiting for, the battery comes up.

I like it !

mine seems to work fine but I agree I find it mostly useless.  I'd rather just look at the actual stress values, they do seem to be fairly on-point.

But the overall problem with stuff like this is that it isn't actionable - meaning what exactly am I supposed to do with this stuff aside from adding to all my other naval-gazing metrics?

Most days, I'd agree it's not actionable.

There are some edge cases though. One that comes to mind: high HRV stress and a depleted body battery, despite diet, sleep, psychological stress being "normal": sign you're getting sick. I've witnessed this firsthand before any symptoms showed up.

Yeah that's a good point.  Again though, what action can you take just knowing you're getting sick soon?  I suppose you could stop training, but if you're actually getting sick then it's coming no matter what you do anyway.

The same for me since 4 days ago. I only had two christimas dinners, but 5% for four days is too much

In my case: I could have gone to the hospital sooner. After a single dose of antibiotics, my fever went down and Body Battery started recharging. It was eerie how immediate it was. (yes, I completed a full course)

Another edge case: dehydration or not enough electrolyte intake will cause elevated HRV stress and low Body Battery. If you're doing long-distance hiking in hot weather and wake up to a flat Body Battery, it's an indicator you need oral-rehydration solution and maybe take a rest day off trail.

So, yeah, most days Body Battery may not be exciting but knowing what trends to look for can save you from a world of hurt.

Yeah i guess those could represent some edge cases.  Frankly I don't trust its accuracy enough in my case to have it override my general overall "senses" in those instances though.  I see far too many false positives (or negatives) with the body battery to come close to trusting it.

It would be nice to be able to use it to guide training (i.e. "you're free to do those intervals today!" or "better take it easy or use a rest a day") but we're not there yet I don't think.