How to Charge an 18V Battery
A battery that is labeled as an 18 volt battery is made up of 1.2 volt cells. There are 15 of these cells in the battery that are linked together to give the battery its power. Keeping the battery properly charged will help the battery last longer and maintain more power in the long run.
Determine what kind of charger you have and how it will charge the 18 volt battery. Some chargers require you to connect the battery to the charger with an input jack, while other chargers may require that you actually insert the battery into the charger.
Set the charger to 18 volts. You will only have to do this if the battery charger is made for batteries with different voltages. Setting the voltage too high may damage your battery. Setting it too low will not properly charge your battery.
Turn on your battery charger. Some chargers do not have to be manually turned on. They are powered up as soon as they are plugged into a power source.
Let the battery charge until it is full. The time this will takes depends on how depleted the battery was when you started charging it. If it was completely drained, then let it charge for at least two hours. If the battery has not charged after three hours, then the battery needs to be replaced.
Turn off the battery charger when the battery is full charged. If the battery charger does not turn on manually, then unplug it. Remove your battery from the charger.