Today I used my watch in fitness tracker mode for nearly two hours. The heart rate monitor was running but I don't know about the GPS because I was also carrying my phone. I guess there's no way to know what device had the GPS active.
I've just put it on charge and it had only dropped to 74%. With the old watch, at the end of each day, it was normally between 40% and 50%
I need to repeat this but leave my phone at home.