To protect my 2 x 6v Trojan Batteries, I bought and installed a Schneider Xantrex C35 Charge Controller.
The Controller is fairly easy to setup and it comes with a comprehensive manual. It's very difficult to get stuck with the installation or wrongly configure the controller.
I installed a dump load to divert excessive power. I still have to find or build an aluminium box for the diversion load heater, in fact right now it's just hanging underneath the controller. The dump load can easily handle 12 amp at 12v.
I have installed the controller a month ago and I can confirm that the batteries have never been overcharged. In this small installation I do have more power then needed and therefore without the controller I'll be boiling the batteries on a daily basis.
The photo below is displaying the 12v Control box and next to it the charge controller.
The dump load has been enclosed in a box...