I have wanted something like this for controlling the panels on my sailboat, and at one time built a very basic one from a design in one of the older handbooks.  It worked fine but I wanted something a little more sophisticated.

Some of the parts I had, others I ordered from DC Electronic's and DigiKey.  I built it ugly and slightly Manhattanish.  The result was something that I fit into a small plastic case, measuring 3"x 2 1/4"x 1 1/4".

I sorta did some tests and finally put in on the boat, where it has been for about a month.  I have not mounted it permanetly since I am still "testing".  

Three LED's on the front of the case indicate whether the batteries are charging, or charged or if the panels are not on-line (night or cloudy days).  I have included some pictures, but forgot to take one of the front!