King Air 200/B200 Practice Exam

During external power, the battery helps damp and limit voltage transients hitting the aircraft’s electrical system. Keeping the BAT switch ON connects the battery to the DC bus so it can act as a buffer, absorbing spikes from the external power source and smoothing the bus voltage. This protection helps prevent damage to avionics and other sensitive equipment that can be stressed by sudden voltage surges. If the battery were disconnected, there would be less buffering, increasing the risk of spike-related problems.