There seem to be a lot of reports of high battery drain and instability lately.
The FIRST thing Garmin support is going to ask you: "Do you have third-party apps installed?" This means watch-faces, widgets, datafields, whatever. REMOVE THEM.
Respect to the diligent devs like Hiking Jim (Hike2 app) and TheCodeDude (Barcode Wallet app) but no third-party app is going to have the same level of testing as stock Garmin software - it just can't. Firmware updates are more likely to break third-party software so even if something is working fine "for now," it may not tomorrow.
Disclosure: I do use "Barcode Wallet" and have had no issues with it. (it's "static", unlike a watch-face).
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UN-related to battery drain: wear your watch correctly. I see a lot of photos of people wearing them right at their wrist. It's supposed to be about two-inches up your arm, well away from the bony protrusion in your wrist, per this entry in the manual: https://www8.garmin.com/manuals/webhelp/forerunner945/EN-US/GUID-F2E7E0A9-FB44-4297-BF4D-D0C31C400C45.html
Wearing your watch too close to your wrist will screw up HR and HRV readings which in turn bork the metrics for all sorts of things like Stress, and Body Battery which is driven by HRV stress. Further, it may also mess with sleep tracking as the watch measures wrist-actography.
If you're wearing a chest-strap HRM, watch position during an activity isn't as important as optical-HR will be disabled. (you can even stuff your watch in a pocket - ultra-runners will do this, and plug their watch into a USB powerbank to charge)