According to those sources (via 9to5), Apple's S1 chip will be close in performance to the A5 processor of previous iOS devices, but that the powerful processor and high-end display will lead to major battery drain.
Apple wanted about 19 hours of use if the user was "mixing a comparatively small amount of active use with a larger amount of passive use" or up to 4 hours of "active application use" or 4 days in sleeping mode (meaning you are just telling the time).
It seems, however, that Apple could not achieve any of their goals. Instead the Apple Watch will have 2.5 hours of heavy app use, 3.5 hours of standard app use, and 2-3 days of standby mode.
At $349 at minimum, the newly reported battery life is not impressive but we will learn more in March.