batery drain after upgrading to s/w v.11 ?

You might be better asking in the Fenix 5 forum, this one is inhabited by those with the plus models!

It's not a general problem - my battery life is just fine under 11.0

However, sometimes the update process can leave stray code, which can cause the processor to work harder than it should, a cause battery drain.

I'd recommend trying:
1. A soft reset (accessible throught the controls menu, then press the Light button to turn it back on). This method preserves your existing data.
2. If that doesn't work, try the more drastic factory reset (which will erase your existing data).

Hard reset / factory reset:
Turn OFF the Fenix
Press and HOLD LAP button
Power on (still holding the LAP button)
You will get the menu “Clean user data: Yes/No?” release LAP button
Choose yes

Same problem here, buyed on July 2018, worked like a charm with 14 days of battery, but since I update it to 11, battery drain raised to 20% each day with the same configuration.

Neither hard reset fix the drain of battery, at least for me ... did it 2 times and battery drain remains in the same way.

As official Garmin support told my I hard reset the device, so no apps of strange watchfaces installed. Result: 0.7% battery drain in one hour, it's 17% in a day, it's only 6 days of battery without touching it.

Same here. Blutooth turned of about 10 days battery. Before 11.0 update i had blutooth and notifications on a i had 14 days battery life. No apps och watchfaces instlled

F5, 11 months old. On 11.57 Beta. Dropping 4 - 5% a day, just a bit more than when it was new (around 3-4% a day).
Obviously without using GPS but otherwise everything is switched on, BT, HR etc.

Like Dimas_sc and other colleages said, all the basic things, no other watchfaces loaded instead of the default ones, before 11, only BT and HR ... 14 days of battery life, upgrade to 11.0 and the battery drain went off, I had to turn off the BT to have less drain.

On Thursday updated now to 11.57 and after a full reset, it seems to be less drain, now 0.5 per hour, so at least in my case (go from 5 to 8 days), I can say quite clearly that it was a problem with the update, because I have the same configuration and now it has 0.5 less battery discharge per hour, but still far from the performance that the clock had at v10.