A charge controller, or solar controller, regulates the voltage and current coming from your solar panels to your batteries. Cathodic protection controllers are for industrial underground corrosion protection systems only
Depending on the type and brand, solar panels put out 16 to 70+ DC volts, so if there is no regulation the batteries may be damaged from overcharging. Generally, there is no need for a charge controller with the small 1 to 5 watt trickle charge panels. A rough rule is that if the panel puts out 1/60th or less per day of the rated battery amp-hour capacity, you don't need one.
If you are using higher voltage solar panels or panels in series, you will probably need one of the Morningstar, Outback Power, Midnite Solar, or Schneider Electric XW MPPT type charge controllers. Most of the Blue Sky MPPT charge controllers will not handle high voltage series panel setups.
Testing charge controllers: Nearly all charge controllers REQUIRE that they be hooked up to a battery in order to operate. You cannot hook up a solar panel to the input and use the LOAD or OUTPUT with no battery connected. Also, if you try to measure the volts or amps on those terminals with no battery, you will not get a valid reading.
** All About Charge Controllers ** - Not sure what a charge controller is, or what type you need, of if you even need one? Then read our Charge Controller FAQ first.
Not sure what MPPT is and why it is neat? Read this page about power tracking controllers in our technical information section.