That current rating is for nearly a short circuit, and not likely accurate.
I don't see it being able to overcharge a 12 volt battery. With a diode in series, the chargeing voltage would be about 15.2 volts.
In the setup I have with the trailers, they are out in the sun all year-round, and none of the batteries have had a problem. The current is too low to hurt the batteries. The batteries I use are deep cycle golf-cart batteries, 6 volts each, 2 in series, 4 sets like this, giving 880 AH capacity.
The simplest regulator I have seen is simply a pass transistor, say a TIP120 or similar, and a small trimmer pot on the base. Once the voltage drops to about 12 volts, the transistor is nearly off. The thing is though, in full sunlight the whole circuit is the equivalent of 2 diodes in series with the batteries ( the C- E junction drop .)
Unless you are charging really small batteries, ( in which case you don't need such a large solar panel ) there is little chance of over charging the batteries.
edit - bah! Nigel types faster than me - again