Another battery drain case (with plot twist)

Hi everyone:

So... another FR255 user here with high battery drain (specially noticeable during night). I've seen a lot of posts lately about this topic, and this one might be a little different. Let me explain.

My watch is set-up as any other: continuous pulse-ox, nothing strange (any question about this, is welcome). Of course, no official solution works: resetting, hard resetting, factory restore... whatever Garmin says... it does not work.

I have algo sent my watch to Garmin to review it (12-26 july 2024), and they updated it (to 19.18, which already was the version it had), and returned it. After all, it is behaving exactly the same: high battery drain.

The thing is that I decided to do some tests myself (engineering background, you know) and, even though I still don't know the cause, I have isolated my problem to exactly 1 action that triggers the battery drain and a fairly simple solution that works 100% of the time (although I have to repeat the "solution" every time I trigger the problem).

Let me explain:

I have identified (I know this is no secret, it's just my finding, just let me explain everything) that the HR sensor has 2 working modes:

1. "Rest" mode: it is the default working mode, and allows the watch to save battery. It is less precise reading HR and so on, but is battery-economic. You can identify the HR sensor is in "rest" mode if you slightly lift your watch from your sking and see the red/green lights flashing (clearly turning on-off continuously). You need to have an HR pulse below 90-100 to see the rest mode.
2. "Active" mode: this is the mode in which the HR sensor gives does best reading pulse from your wrist. The most sensitive mode, but also the most batter drainer. You can identify this mode because green/red lights are fully on, no blinking/flashing happens. You can see the HR sensor in this mode if you slightly lift the watch from the skin while recording an activity or with an HR pulse over 90-100 bpm. 

The watch transitions automatically between rest and active modes.

And, as you have supposed by this time, the battery-drain problem (in my case) is with the HR sensor being stuck in active mode, and not returning to rest mode.

Now lets talk about what triggers my HR sensor to block indefinitely in active mode, and this is what might be useful to you.

The process is simple and (for me) it gets blocked in active mode every time, 100% of the time:

1. I use the watch normally, do nothing special. Wear it, record activities, etc., none of this affects the HR sensor or blocks it.
2. I let it drain battery normally, and charge it, again, as usual.
3. About 40-60% remaining battery, I usually connect it to the charger (original Garmin cable, btw). And I always charge it to 100%.
4. Disconnect it, and wear it again.

And that's it. By step 4, after charging and disconnecting, I can clearly observe that battery runs out at about 25% per night (normal value: ~5% per night). Just charging it is what triggers my HR sensor to go full blast all the way, all the time, draining battery in about 2-3 days.

And now, the solution I have found to work 100% of the time:

It never works to restart/reset the watch after disconnecting it from charger. HR sensor gets stuck in active mode forever (forever = while battery lasts...).

But, (it works right away or hours later of disconnecting charger, it does not matter), whenever I do these steps, the sensor returns to rest mode and the battery lasts about 6-7 days (remember I have continuous pulseox enabled, so I accept it does drain a bit faster than normal):

1. Go to watch face
2. Press start/stop to enter activity selection
3. Press start/stop to select an activity (I use "run", which is my default)
4. Let the watch show the activity's initial screen (the one with the red/green GPS rounded bar at the top)
5. Press back until it returns to watch face

That's it. Just going into an activity and back to watch face triggers the HR sensor to reset it's working mode and return to rest mode. I just need to do this right after disconnecting charger, and the HR sensor will work in rest/active mode flawlessly until next charge, when I need to repeat this. (After doing this, the HR sensor might take a minute or so in active mode, before returning to rest mode. Be patient!)

As I previously said, I tried to contact Garmin, I even sent it to them, and they found nothing. Because their protocol is just "firmware update and return to customer". They do not do anything else.

I know that many of you have battery drain issues, and maybe some have the same problem as I have, and I just wanted to share my experience and my "temporal" solution, which, at least, allows me to have a fully functional watch with just a very simple step.

And I hope Garmin finally reads this and takes it seriously, because it did not happen when I bought the watch, it started happening after a firmware update (cannot say exactly which one, but have been experiencing this, at least, since version 18).

Ah, I forgot to mention that I'm no beta-software tester/user. All my firmware upgrades have been to public rolled out versions.