If your alternator fails, how long can you expect your battery to last?

In the event of an alternator failure, the duration your battery can sustain electrical power is generally expected to be around 30 minutes under normal flying conditions. This duration can vary based on the specific aircraft and its electrical load, but 30 minutes is a standard estimate for many light aircraft.

During this time, the battery will continue to power critical systems such as communication radios, navigation equipment, and essential flight instruments. However, it is important to note that the actual time may be shorter if the aircraft is utilizing high-draw electrical devices, such as landing lights or cabin heat, which can increase the load on the battery.

After the alternator fails, pilots are trained to manage their electrical load effectively by turning off non-essential equipment, maximizing the available battery life. Understanding this allows pilots to plan for a safe landing and potentially avoid undesirable situations caused by total electrical failure.