Hook the red positive clamp to the positive battery terminal (in or out of the car) without the battery charger being plugged into an outlet or the power button turned on. Some battery chargers do not have a power button and automatically turn on when plugged in. Hook the negative clamp to the negative battery terminal.

Read all the other switches before powering up the charger for the correct options. Most chargers have switch options for amp settings and battery types. Some more elaborate chargers may offer different volt settings. For a car battery, you need to switch to conventional battery or non-deep-cycle battery. You want to switch the volt setting (some chargers automatically come equipped with only a 12-volt charging option, as most car batteries are 12 volt) to 12 volts. Last, the amp setting option depends on how quickly or slowly you want to charge the battery. The lower the amperage, the longer the charge will take; the higher the setting, the less time the charge will take. On some chargers, there may also even be a high or "start" option, and this can be used to jump-start your car battery using the charger. Place the amp setting to accommodate your desired task with the battery.

Plug the battery charger in, and or turn on the power button. In some cases, turning a timer dial will power up the charger after it's been plugged in. This timer can be set for any amount of time you wish to charge the battery and will automatically power down the charger when the time expires.