[delphin]

Indeed as elcreative has said, there is no down side to this.

In fact Lithium batteries like to be 'topped off' like this and will actually last longer with partial charge/discharge cycles than with deeper cycles.

So don't worry about the fact that your reader is charging every time you plug in the USB.

You can either do just a partial charge or a full charge, and things will be just fine, so you also don't need to worry about removing the charger before it reaches full charge.