A method for detecting a discharge condition fault in an electrical system of a vehicle or a piece of machinery includes supplying electrical energy to the electrical system from an auxiliary battery or batteries of a multiple battery system when a main battery of the multiple battery system does not have sufficient power to start the vehicle or piece of machinery. The supply of electrical energy from the auxiliary battery or batteries is sufficient to at least enable the vehicle or piece of machinery to start. After the vehicle or piece of machinery has been started using the auxiliary battery or batteries, electrical energy is supplied to the electrical system from the main battery. A general operating fault is determined to exist in the electrical system in the event that the vehicle or piece of machinery stops running after being supplied electrical energy from the main battery.