Charging a spare car battery is an easy job that only requires a battery charger, a power outlet and a little time. There is no inconvenience, for there is no need to get the charger to the car which often requires one or more extension cords. Rather, the spare battery can be set right next to the charger on your workbench or porch.
Charge a Spare Car Battery
Set your spare car battery on the workbench or clear area for charging. Next to it place your battery charger and set the switch to 12 volts. Most car batteries are 12 volts, so unless you know otherwise, do not set it to 6 volts. Do not plug the charger in quite yet. If the battery terminals have rubber plugs over them, remove them.
Attach the red clamp on the charger to the positive terminal on the battery. Next attach the black clamp to the negative terminal. Plug the charger in to the wall outlet. If there is an ON/OFF switch, turn it on. Otherwise it will automatically engage when plugged in.
Now all you have to do is wait. Depending on how low the spare battery is, it could take a few hours for it to be fully charged. When it has reached 100 percent, unplug the charger from the outlet then disconnect the clamps. Put the charger away, replace the plugs back on the terminals, and set the spare battery somewhere out of the way.