The Pro X-SP model has a new surge "spike" protection circuit that adds additional protection to the electrical system. As electronics take over more and more of automotive vehicle operations, voltage spikes are an increasing problem. Transient voltage "spikes" can cause damage to computers, two-way radios, MDT equipment, cameras and a host of other electrical equipment. With PriorityStart! Pro X-SP, the battery voltage is monitored at all times. When the vehicle is off, if the battery voltage drops below approximately 11.8 volts, the battery is disconnected leaving starting power (the battery voltage immediately recovers). When the vehicle operator returns, he simply operates the headlight switch or steps on the brake pedal to cause the reconnection.