Solar Trickle Charger

I just installed a 25 watt solar panel on my boat to keep the batteries fresh. I also installed a controller to make sure the batteries don't overcharge. The panel output was 21 volts before the controller according to my multimeter, after the controller it is also 21 volts. I would expect the output from the controller to be more like 14.5 volts. When connected to the batteries it drops to 11.8 ( the batteries are discharged) and the controller reads "charging". Is this normal?