The voltages can range from 7 to 28 volts, the higher the voltage the more powerful the tool. The voltage can help you find the battery that is best suited for the work that you are doing. Depending on how long you are working the voltage will give you a good idea of the batteries running time. Light workload: 7 volts – 15 volts Medium workload: 12 volts – 18 volts Heavy workload: 18 volts – 36 volts