Fenix 8 Amoled takes 20% battery for one night

Restart the watch. 

tomshanti said:

Reset with long button press upper left did not help

I had the same issue — battery drain of 7% per hour. After two days, the wrist heart rate sensor stopped working. I tried everything — factory reset, etc. — but nothing helped. Eventually, I replaced the watch, and the new one doesn’t have these problems.

However, there’s one thing I didn’t try. There’s a hidden menu: go to Settings > System > About, then press the upper left button five times quickly. In that menu, there’s an option to reinstall the software — maybe give that a try, it might help.

Wait until the latest beta goes public and they removed the auto battery saver at night option. Battery life on the 47mm Solar is shyte already, now I have to remember to manually turn it on every night. 

After a night of 2% battery use, yesterday it happened again but battery drain started already during the evening:

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You can try restarting the watch before sleep to see if something is stuck on.

Or turn on battery saver at night, and see if it helps. If you already had it on, as Piotr mentioned, try a reinstall. You don't have to redo any settings. 

Restart helps but after some hour it again starts battery draining: 

First hours after full charge was a 4h GPS tracking  then you can see the small decline of a few percent over many hours. suddenly it starts battery draining without any config change or activity. It consumes almost 50% in a few hours. At the lower right after the steep decline I restarted the watch and you can see it progresses with much less battery usage.

I also noticed that gesture stop working during the battery draining period and that despite I am using the screen it switches the screen of after the gesture timeout seconds I configured. Restarting the watch also brings back gesture and screen to work as expected  

Solution could be very simple: uninstall unnecessary apps like battery monitor showed in the picture or non-facotry watchfaces.

I installed battery monitor to exactly make the issue visible and troubleshoot. 

Is your phone android or iOS?  I changed from Samsung to iPhone and my battery increased a lot. 36 hours only dropped 2 %. Without any solar(rainy days )Hr on. Sleeps mode on. With Samsung I lost around 3,5. % per 24 hours with around 40k solar . Notifications of. Tested during no gps activity