Probably bad battery then.
Engadget got 8.5 hours with continuous video in their testing: (Battery life according to HP is 9 hours for continuous video playback, and in our test (WiFi on, Bluetooth off, video looping) we came close to that: just over eight and a half hours)
Anandtech got only 6.5 hours with the heavy usage test: (In our light multitasking battery life test we're constantly checking a Gmail account, playing music and running through our standard smartphone battery life test. All tablets here are set to nearly the same brightness using our colorimeter to ensure a level playing field)
So even in the worse case scenario, it's pretty reasonable.
Of course, you still haven't bothered to give actual numbers so who knows what your problem is.