An adapter comprises an input port being coupleable with a single-voltage output interface of a single-voltage battery pack or a multi-voltage output interface of a multi-voltage battery pack, an output port electrically connected to the input port and being coupleable with a single-voltage input interface of a first power tool or a multi-voltage input interface of a second power tool, a switching mechanism being switchable between a first state and a second state. When the switching mechanism is in the first state, the input port is coupled with the single-voltage output interface and the output port is coupled with the multi-voltage input interface of the second power tool, when the switching mechanism is in the second state, the input port is coupled with the multi-voltage output interface and the output port is coupled with the single-voltage input interface of the first power tool.