I'm not too sure what the fuzz is about with the replaceable battery. I've had my first Sony for over a year now and battery is not an issue. I also replaced my first reader already and think I probably will do this again once there is a wider selection of readers offering 8"+ screens for a reasonable price. Then again, the battery on my current Sony won't be an issue.
To replace the battery of the two Sonys I own you have to tinker a little with the hardware, but I'm sure I could get it replaced if need be. I already saw a battery for the 505 for around $10. Sure, if you send it in to Sony, you can also buy a new reader instead.