I am not so sure that controller is no good. IMO give it more of a chance, then decide.
The controller is supposed to get the battery to the set high point voltage (14.6 in this case) and hold it there while amps then taper till the battery is full. It holds it there by switching on and off (as seen on your monitor I think) so the "average" voltage the battery sees is 14.6. (bouncing between panel voltage and battery voltage)
Before that controlling starts the controller does nothing except pass panel charging to the battery, while the battery voltage rises.
Panel voltage will be somewhere in the high teens, depending on a bunch of things for how much at any time.
Some controllers will have a time they stay at the 14.6 and then they drop to 13.x Float voltage. In any case, darkness arrives to end the 14.6 and battery voltage drops right off to 12.x so you get a Float in there no matter what.
