iAudio4 battery lifetime

[theDuke]

I'm using the iAudio 4 (512 MB) now for about three months and the only thing I must complain is the battery lifetime.
The product description states that battery lifetime is up to 15 hours, but I only get a maximum of 7 hours from batteries and about 5 hours with rechargeables.
I have disabled all energy consuming options (backlight) and I use only CBR encoded MP3.
But what troubles me most is, that the iAudio is discharging the battery without even using it. A full rechargeable was empty after two weeks in the iAudio 4 without ever switching the unit on.

Is this normal or is my iAudio defect an I should exchange it?

Also the battery status display is absolutly wrong, displaying full for four hours, but dropping to empty in less then one hour (for rechargeables).
And if voltage display is around 1.10 Volt the iAudio stops playing, is this normal too?

I also proposed a energy saving mode for the firmware with less/no info (I guess the dynamic peak level and title scrolling consumes extra CPU power) to be displayed at the LCD. This would be great, because most of the time I do just listen and never look at the LCD.

What do you think?