The last report I read about the battery life stated that we'd be lucky to make it until lunchtime without having to recharge it!
From 9to5mac website:-
Apple had originally suggested that the Watch would need to be charged nightly. Somewhat of a pain, but given that most people charge their phones each night, not the end of the world. Instead, the following has been cited:
displaying the clock face alone (with ticking hand etc) will provide for 3 hours of use
heavy app use will provide 2.5 hours of use
standard app use will provide 3.5 hours
using it as a fitness tracker will provide 4 hours of use
This will be a disaster if true!