I know nothing about CTEK chargers other than they have an excellent reputation.

What I do know, in "normal" cars alternators charge at 14.4 volts when a battery needs topping up which drops to about 14.1 or 14.2 volts in normal running with no famcy consumers switched on.

So based on that 14.4 volts after turning the charger on is perfectly normal.

The Ctek chargers (or any car battery charger for that matter) do not increase the battery's voltage above what is the normal charged voltage (approx 12.7 Volts).

To charge a battery you need to have a forward voltage that is greater than the battery's normal working voltage, if there was no forward voltage then there would be no current flow from the charger to the battery and charging would not occur.

As you can see the forward voltage is the chargers output voltage minus the battery's voltage which is approx 2 volts.

There are three basic phases for a smart charger.

They start with constant current (at the charger rating) which means the voltage starts low and rises to c. 14.4V. The voltage remains there as the battery continues to charge and the current drops. When current has dropped to a trickle the charger goes into pulse or maintenance mode. It's this last phase that means you can leave it connected.

Some will do a pulsing phase to start with which is associated with desulphation.

You should be able to leave it connected. I have one on a fair-weather car that isn't used regularly, does short journeys and has a small battery just for good measure (it's an old MX5 with a c. 30Ah gel battery). I'd say the battery is performing better now than it was when I bought the car in 2011... not sure how that works!