Vivoactive 4 switching off during activity

Exact same thing happens with mine. Have not had any luck with a fix. Lots of people seem to be having the same problem. Garmin folks don’t seem to have an answer/solution. Pretty disappointing as the VA4 wasn’t cheap. Good luck with trying to get somewhere.

Mine just did this for the first time yesterday. A 45 minute jog was recorded as 5 minutes, barely 600 steps. When I looked at my watch step count however had recorded around 4500 steps for the 45 minute period. I hope this doesn't become a habit. I am already looking around for a new watch but didn't want to be rushed. I hope the 5 comes out sometime soon, although there a things about Garmin I am unhappy with and after so many years,  am considering moving to something else entirely. 

I suppose battery is dead. I have the same issue, not only during activity but for example during NFC payment. Even in standby when battery drops to 55-60% it suddenly switch off.

There is a video on YouTube of battery replacement, but it is not an easy operation at all - first step is removing display using heat gun

I have the same issue, but only with the lastest FW 7.80. I will try to downgrade...

Interesting, I admit I have lost track of new firmwares. Please give us a feedback if downgrade helps

My VA4 was turning off every time that I pressed START for an activity, regardless of battery %. Had to plug in to charger to get it to start again. Read a comment on a very similar thread to this. Comment said to turn off Vibration. I turned off Vibration. It seems to have fixed the problem. Time will tell???

Ok, I can confirm my issue was caused by dead battery. All symptoms are gone after battery replacement

Who replaced your battery and is your watch now still waterproof? Keen to try to get mine replaced too. Cheers.

Local service center here in Czech republic. They glued it again so it should be waterproof but with no warranty. Tried it in shower and rain and seemed to be fine, not planning to swim with them though