Whether cold weather from a blizzard has caused a car battery to run down, or the battery has died in an isolated location, batteries sometimes need charging when AC power from a home or garage is not available. Fortunately, you can also use a gas generator to recharge a battery, if you also have access to a battery charger. The generator produces the AC power needed by the battery charger, and the battery charger then converts the AC power to DC power to charge the battery.
Check the fluid levels in the generator. Correct any that are low. Connect the red positive wire from the battery charger to the positive terminal of the battery. Connect the black negative wire from the battery charger to the negative terminal of the battery.
Verify that the battery charger is turned off. Start the generator by pulling the start cord or using the starter switch.Once the generator starts wait a minute or two for the engine speed and voltage to stabilise. Waiting for the speed and voltage to stabilise is important because it helps to keep voltage spikes from damaging equipment connected to the generator, such as the battery charger.
Plug the battery charger into the 110-120 volt AC outlet on the generator. Turn the battery charger to the "on" position. The battery charger and generator should be charging the battery.
A DC generator can also be used to charge a car battery without a battery charger, but controlling the generator's output voltage becomes more important in that configuration. If the voltage is too low, the battery will not charge. If the voltage is too high, the battery could be damaged or explode. This method is not used very often.