Every charging source requires a controller (regulator) to prevent a battery from overcharging. In the case of a PV system it is also essential to prevent reverse current flow during the night, discharging the batteries. This is prevented by placing either a relay switch which opens when no more charge is coming in from the solar panels, or by using a diode in the controller which acts as a one-way valve for electricity. If batteries are constantly overcharged the life of the battery will decrease dramatically. A controller will sense the load of the battery and prevent further charge entering into the battery once it senses that that battery has reached it's capacity. The only time when a system does not require a regulator is when the PV panel produces 1.5% of the battery's amapacity (Example: a PV panel which produces 1.5 Amps charging into a 100 Amp/hour battery). Controllers may also contain an automatic load disconnect, which prevents the user from using the battery once the battery voltage is low. Certain controllers will also have temperature compensation (necessary for when batteries are not in a climate controlled area). Good quality regulators will regulate the amount of electricity going in and out of the battery more efficiently, extending the life of the battery.