I think one CAN turn of the HR monitor, in privacy and fitness.. just move that toggle to off. This was discussed prior to wOS2 coming out.
As for power, I find that in general use the watch loses about 3% an hour, but in a workout it loses between about 9 and 11% an hour.
I've done 5+ hour workouts with all HR being tracked, what, every 6 seconds or something? And had about 50% battery life left.