Battery suddenly runs down very fast

Try disabling individual components (Bluetooth, backlight/display, alarms, vibration, GPS, PulseOx, ...), and also disable any CIQ apps or watch faces if you use any, perhaps you can isolate the culprit. 

The watch will not charge beyond 48%. I have watched it charging for the past half hour and the battery indicator reaches 48%, then quickly drops to 47%, then struggles to reach 48% again and then drops back. This happened for the full half hour. 

Even if there were some rogue app or software update, it would not cause this charging behavior.

Unfortunately I think the battery has reached end of life.  It's strange to me that it happened so suddenly, but what do I know about batteries. 

Facing the same issue after the GCM 4.65.1 update and the FR945 11.x update... I have lost blue tooth connectivity and the watch wont pair under any circumstances. All this happened after 2 years working flawlessly. Frustrating.

When experiencing sudden battery drain after a firmware update, follow the steps described in the article Why is My fenix 5 Series Watch Battery Draining Quickly? | Garmin Customer Support (never mind the different model, the principle remains the same at other models too): Soft Reset + going through the full charging cycle. If it does not help, contact the Support.

So here is the latest on my Garmin Forerunner watch that suddenly had the battery discharge at an extremely high rate.

First of all, let me thank trux for all of the helpful problem solving suggestions. I did not act on any of them because I have not made any changes to the apps or software or firmware on the watch. If the problem had persisted I would definitely have used those suggestions for troubleshooting.

Yesterday evening I left the watch on charge for another 4 hours, and by the time I went to bed it had struggled to reach 76%. As I turned off the watch for the night I could see the battery percentage dropping from moment to moment. 

The watch was turned off for about 9 hours overnight. When I turned it back on the battery indicator showed just 3%. I have never seen it drop even 2% overnight when turned off.

I connected the watch to the charging cable and plugged in the charger as usual. This time to my surprise, the watch charged quickly to 98%, at which point I took it to go exercise. Having exercised intensely for 20 minutes, and then moving around through the morning as I usually do, with about 5,000 steps recorded, the watch is at 87%. In other words, the watch "has fixed itself" without me disabling any features or conducting further resets.

I think it is important to state what I was doing right before the watch suddenly started losing battery power. For reasons I won't go into here, immediately beforehand I had been cycling for over 30 minutes along a trail that is right below two giant high voltage transmission lines. I always avoid powerlines but in this case I had no other way to reach my destination without going on extremely busy roads with no cycling lanes. It is my conjecture (and I can't prove it) that spending that much time under such a high intensity magnetic field may have caused the battery circuit in the watch to behave abnormally. 

Now it is back to normal. I speculate that leaving the watch off all night was enough to allow the battery circuit to reset itself.

I can tell you that I won't be walking/riding under high voltage power lines again, even though I understand that coincidence is not proof of causality.

You are a mine of good information.  I stand corrected.  Thank you for taking the time to point out the real reason for this problem. 

Same here since last update.

Battery will drain within one day on Instinct 2 solar surf!!

Seems to constantly disconnect from my phone also

JVu said:

Same here since last update.

And did you follow the instructions from my previous post?

Battery completely died.

Recharged to 100%.

Still dying just as fast