Battery drop and no HR

Hi, 

I have got a Fenix 5. I disabled automatic updates and stayed on v 13.3 and everything was ok. But 1 week ago, my battery suddenly dropped from 50% to 10% within some minutes and then to 0% after 1 hour. In addition, the watch didn't measure my HR after dropping under 50%. I thought this would be solved with an update and updated to v 15.00, but I now have the same problems. 

Could you please correct that via software or do I have to return the device? 

BR,

Bernhard