battery not keeping 100% even if connected to power

Hi,

besides the problem of loosing to much power to fast, i found a second problem while charging the iPhone4S.

I switched on the battery indicator with percent.

So i connect the phone to cable with a usb port of my PC. The phone starts charging. When it reaches 100% it does not seem to keep the power.

On the next morning I sometimes only see 99%, 97%, or even less.

If i unplug the phone and reconnect it it starts charging at once.

The old iphone4 used the same USB port and never had that problem.

So maybe the part controling the charging of an iPhone is also not working correctly.

Markus