I leaved my DX100 slept for about 5 hours, and the battery drained from 98% to 93%. I think this is pretty acceptable.

Today I go back to this thread and find so many people complain about this DAP, and I would like to say something about it.   Actually I'm a user of DX100 in China. According to the shop which sold the DX to me, this DAP is always out of stock in China, even the Demo in the shop was bought...