PV voltage on solar charge controller always 13V
The Solar panel voltage is being held to 13V because it is supplying current to the battery to charge it.

That is expected behavior, and not at all harmful to the panel.

As the battery reaches full charge the load on the panel will reduce and its voltage will rise.

Some designs of solar charge controllers will control the power by diverting the panel power into either a resistor or a short circuit in which case the panel voltage may reduce or even cyclically pulse to zero.