FCC Technician Exam Question Of The Day (T0A08)

Q) What is one way to recharge a 12-volt lead-acid station battery if the commercial power is out?

A) Connect the battery to a car's battery and run the engine

NJ2X Notes:
A car has an electrical generator that is used to maintain the vehicle's battery.  This can be leveraged to also recharge a 12-volt battery for amateur radio use in an emergency.