The idea is to keep the aircraft powered while you remove the faulty source from duty. In a dual-generator system, you isolate a suspected bad generator by using its control switch to take it offline and, if available, the bus-tie logic to separate the generator’s bus from the rest of the electrical system. This prevents backfeeding and fault propagation while the remaining healthy source (the other generator or external power) continues to supply power to the essential buses. After placing the suspect unit offline, you verify that bus voltage on the remaining powered buses stays within spec using the other source. If the voltage looks good, you can continue with a normal configuration and plan further maintenance later. Shutting down the entire electrical system would cut power to critical equipment. Removing the battery isn’t the standard way to isolate a generator and can cause unintended power loss to essential systems. Disconnecting all loads isn’t how you isolate a generator either and could lead to unstable system voltages or unnecessary loss of critical services.