The main function of a charge controller or regulator is to protect your battery from overcharge and block a reverse current. If a non-self-regulating solar array is connected to lead acid batteries with no overcharge protection, the life of your batteries will be compromised. Simple controllers contain a transistor that shunt the PV charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set reconnect is reached, opens the shunt, allowing charging to resume.