If it does come with a "controller" it should be in the black box on the back of the panel (if there is one). Worth a quick look under the lid if it easily removable - might save yourself $30.00.
I'd hook it up to a fully charged battery & take some Voltage & Current measurements under various conditions.
A good little experiment.
Stick it in the shade, angle it away from the Sun a bit or something elegant like put a sticker on the glass.
Their Max Voltage & Current was probably measured in the Sahara.
Be our Guinea Pig so we know what to buy.
If it does come with a "controller" it should be in the black box on the back of the panel (if there is one). Worth a quick look under the lid if it easily removable - might save yourself $30.00.
If it's putting out 20VDC then there's no "black box controller" just fork out for a regulator and save yourself the overall headache. 12V batteries need ~13.6V - 14.5V to charge. No more no less, or you risk frying. Mat
My bad, no controller .. just a diode to stop back flow of current (is my guess). So a regulator it is. Now working out the best design (fix the regulator to the boat or make it all portable).
Sunshine Coast - Kevlacat 5.2
The best option for maximum efficiency is to have the regulator close to the batteries. Keep in mind it is not unusual for these regulators to consume a small amount of power so if they have no solar supply they will over time flatten the battery.