A portable alternating current power supply assembly which has an extendable operational period and which provides an external power supply for a tool. It has a power inverter and a removable battery unit which is connectable to the power inverter by a coupling to form the power supply and which when so connected forms a discrete unit. A DC output from the removable battery unit is converted to a pure sine wave AC output from the power supply assembly by the power inverter. The power inverter is separable from the battery unit to provide an operational period for the power supply assembly which is equivalent to that which might be provided using larger AC power supplies which have larger DC voltage batteries and which are part of a sealed unit with the power inverter.
