A system comprising a multi-voltage battery pack for use with tools of different operating voltages, including a housing and a power tool interface shaped and configured to interchangeably (1) mechanically and electrically couple with a first battery pack interface of a first power tool that is configured to operate at a first operating voltage and is of a design that was on sale prior to May 18, 2014 and, and (2) mechanically and electrically couple with a second battery pack interface of a second power tool that is configured to operate at a second operating voltage and is of a design that was not on sale prior to May 18, 2014.