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Fenix 5S Plus sudden increase in battery drain

My ~3yo Fenix 5S Plus suddenly started draining battery much quicker than before (100% to zero in 24h with no activity and all sensors off). I used to be able to go for a week without charging. I cannot tell what triggered the change, if anything at all. I have already tried (to no avail) all the possible factory reset procedures, including the one triggered by pressing all the 4 buttons. Now the watch is on factory settings, except that I disabled everything obvious that could drain battery (HR monitor, bluetooth, wifi, activity tracking).
The only possible remaining lead to an explanation is that in the "Debug" folder of the watch (which apparently survives factory resets), the file ERR_LOG.BAK contains an entry timestamped 7 Jan 2023 (see below) which may be exactly when the issue first appeared. This is the entry:

2900 (fenix 5S Plus) SW ver: 1800
Build Type: RELEASE
Commit:61a9197469189bb7db42684335b898ded6cd291a
ESN: 3977555971
01/07/23 22:39:37
AP
PWR RST CTRL: 0x00000082

Does anyone know how I can access someone able to read what this might mean? I'd love to know whether this may be a clue to the cause of my battery drain problem. Perhaps the watch is gone, but at least if I could tell what behavior or event triggered the problem, I can avoid it in the future. Thanks in advance!

  • Battery Voltage test (battery is completely new):

    Completely charged: 4.3V (it could be ok)

    Completely discharged: 3.4V

  • what does this tell us?

  • I requested the discharge curve to the battery supplier in order to know more about the meaning of the data.

  • They didn't provide me the information.

    By the way, I tried logging to Garmin Connect with a new account. It doesn't work. 

  • Out of interest I bought a bunch of 5S plus from a popular online auction and replaced the battery in all 3 of them with a new battery and charged them simultaneously to 100% and disconnected from the charger they all rapidly depleted to zero within a couple of hours at the same rate

    at some point a bug has been introduced probably in sensor polling which is either irreversible or unknown. I also own a 5 which i replaced the battery at the end of March and has had a handful of charges since then

    As a software engineer I would presume a lot of the core code is shared between devices with  specific modules for input/output read/write code for various hardware components which may differ

    i feel that given the time and tools it wouldn’t take long to debug the code

    regression of firmware may not help as it might be in one of the sub modules for sensors that the issue lies, so unless the main package can regress sensor hub assemblies 

    even if you do regress the first thing GC will try to do is push a new firmware grrrrr

  • Hello, where can I recover the firmware 18? I would like to downgrade. Thank you

  • Locating old firmware versions is like the proverbial needle in a haystack. For all garmins I try to save old versions as and when I find them sadly for the 5S plus I have none but I will keep looking 

    Garmin connect pushes out only new ones unless it’s a beta release which usually includes a previous version as a go back

  • I tested this and pretty sure now it is the battery not fully charging.

  • The question is why?.

  • Something in the software they have to fix and working on now i presume.