I decided to test my Karmas battery life, and well, got about 3.5 hours... And it was that low due to what seems to be a caching problem. My test playlist was all 20 of Paulway's mixes, starting out with the Infinity Mix. This clocks in at almost 4 hours, and what I found is the Karma was constantly spinning up the hard drive, then spinning it back down. Once I noticed this, I quickly switched over to a more normal CD type playlist with short songs, and the hard drive stopped its constant spinup and spindown cycle.
This is with 1.41 firmware.