Inexpensive battery monitors don't do the trick. Relying solely on battery voltage as a state of charge indicator is fault laden.
Get a monitor that actually measures amp hours in and out, such as the BMV 602s like this one : Need A Battery Monitor ? Photo Gallery by Compass Marine at pbase.com
sold by Maine Sail here on sailnet.
I recommend you do some reading and research, you should combine your two batteries into one bank because a single larger bank is able to accept a heavy charge better, more efficiently and faster.
You'll also need to consult some local experts regarding how many amp hours per watt of solar you can expect to produce in your location.