I’ve had some trouble with the lifetime of the battery of my sansa clip.
But now I know what was happening:
I mostly use my sansa clip to listen to the radio.
When I’m back home, I just turn the player off and plug it into the computer and then forget about it.
When I’m done with the computer, I shut it down and I go to bed.
The next day in the morning, I unplug my player and I’m surprised because it’s battery is not full.
This is because when the computer is shut down, the sansa clip detects that it is disconnected and then fall back to radio listening.
So my player was playing radio all night long (without earphones being plugged).
Now that I know that, I have to leave the radio menu before shutting down the sansa clip.
But maybe the next firmware could fix this: when being disconnected, the sansa clip should never fall back to radio mode.