Charge a 12-volt battery by connecting the red lead from the charger to the positive post and the black lead to the negative post. Set the charger to the appropriate charge rate, plug the charger into a power outlet, and allow sufficient time for the battery to charge.
Most 12-volt battery chargers have the option of a 2-amp or a 10-amp charging rate. For overnight charging, select the 2-amp rate, as the higher rate is likely to overcharge the battery if charging continues for more than eight hours. Overcharging a battery leads to potential damage to the battery or a fire. Many 12-volt chargers have the option of charging 6-volt batteries by flipping a switch, so always set the unit to the proper voltage for charging.
A dial on the front of the meter keeps track of the progress as the battery charges. The needle moves slowly from the discharged position to the fully charged position as the battery recharges. When the battery is fully charged, remove the charger by first unplugging it from the outlet and then disconnecting the clamps from the positive and negative posts of the battery. At this point, if the 12-volt battery is installed in a vehicle, it should start using its normal starting procedure.