Same thing happens to me. The watch still had 54% battery life and it just shut off!! Has happened many times. Unacceptable for something this expensive and little support.

TO ALL MY GARMIN FELLAS, I'VE DISCOVERED HOW TO STOP THE SHUT DOWNS (partially) 

My instinct solar was shutting down whenever I started an activity after certain update. I strength train every day and it was driving me crazy. AINT BUYING ANOTHER WATCH 

I'll call this 

*PROGRAMED OBSOLESCENCE*

• Well, I rebooted the watch, paired to a new phone, paired to the PC program, update it, even tried rebooting and not updating it, but nothing. So one day I was running low on battery and I decided to turn off the Bluetooth on my watch, at the next day I forgot to turn it on again, and I trained without any problem, later that day I turned the Bluetooth on again, tried to use it and it started crashing again.

So long story short:

Hold control (left up button)

Find Bluetooth connection and turn it off when you are going to train. 

Ok gracias. Lo probaré. 

Realmente no puedo creerme que no nos den una solución eficaz desde Garmin. Mi reloj aún no ha cumplido ni tres años desde que lo compré.

Garmin Forums Guys fix that issue it's a deal breaker for us to buy another Garmin!!!!!

Hello~ May I know more clearly how to turn off the Bluetooth?

Cause I can't find it in my Garmin Instinct Solar (Not 2).

Thank you so much~

Hold CTRL and look for the Bluetooth logo with a phone. 

Sometimes it works, sometimes it gets worst.

Imagine thinking that screwing people's watches would make the same people buy a new one from the same brand... 

Thank you I have customizing the Controls Menu.

And add the Turn off Bluetooth in the CTRL page.

But unfortunately after turn off the Bluetooth, my Instinct still

Turns off When starting of any activity T-T

This is my first watch of Garmin, just used 1 year and 1 month. The price of Garmin is not low, but the quality and after-service of Garmin is very upset me. The battery issue was totally not a single-owner problem, but I need to pay 1/3 price of a new watch to them for fixing their product design problems.

And pay for AppleCare right?

Same to all of the above, treadmill, swim, whatever, just cuts out.  No response from Garmin when you try their support.  And yes, just over one year old, watch now only good for sometimes being able to tell you the time.  Absolute rubbish, looks like from threads Apple is the way to go. Shame as it WAS a decent watch