Battery draining in 36 hours with no GPS use.

Have you tried rebooting the watch?

First of all, try the soft-reset - holding the Light button until the watch shuts down, then turn it on again. If it does not change, try the full factory reset (find it in the menu, or look it up in the manual).

Yes. It`s did not work.

8514900 said:

I did that too, but the battery life kept getting worst and after the last update the battery life got a lot worst.

Yes, but you should just do it after the last update. Better told, it is wise rebooting or soft-resetting the watch after every firmware update.

If you think it is due to the firmware version, downgrade to an old one. Though, I do not think it is the culprit, since my 3 years old Instinct still has a decent battery life even with the latest firmware version.

There a way to do that?

8514900 said:

There a way to do that?

Downgrade of firmware? Yes, of course. Each beta version of the firmware can be installed from the provided zip file, which also always includes the last stable version, that can be installed too. Just identify the version that you believe would be working for you, search the forum for the closest higher beta version, and then try to find it online, or ask on the forum, whether someone kept the file and would be willing to send it to you. And do not forget to disable the auto-updates in System Settings, to avoid that it gets immediately overwritten.

I agree.  In addition to resetting the watch after an update, I also reboot my phone.  Doing this I have never experienced a battery drain on any of my Garmin watches anytime or after any software update. I also turn off automatic updates and only update via Garmin Express.  That may not work for everyone but I have had good luck so far.