As for the battery life.. if you don't always jump from song to song, the rechargable batteries easily go 10.
If you keep screwing around with the buttons and stuff while playing, then maybe you can get 5.
On a road trip (the only time I ever had to use the battery adaptor) I used a pair of E2 batteries, and it lasted a total of ~26 hours?
This was playing mp3s, and yeah while playing Audio CDs, the battery life decreases noticeably.
Also, the hiss isn't from the remote, if you take out the remote and plug the headphone directly into the headphone port, there will still be the slight hiss.
The line-out seems to be clean though, and even through the headphone port, with a pair of KSC-35s, the hiss is barely noticeable. With the included headphones (which were horrible by the way), the hiss was VERY noticeable.