How can I switch the "battery saver mode" off.

I'm also struggling with the heart rate sensor going on and off during activities. Tried everything to find the issue. At certain time the watch gives a message that it entered "power saving mode" and this correlates well with the heart rate sensor going off. The watch does not have a power management widget like the fenix. I do not know how to switch this function off. Will appreciate help on this topic.