Do Stanley Fatmax Batteries Fit DeWALT? (& Vice Versa!)

Stanley Fatmax power tools and DeWALT are both owned by the Stanley Black & Decker company. This might lead you to believe that Stanley Fatmax batteries will fit DeWALT tools and DeWALT batteries might fit Fatmax tools. But is this true? Let&have a look and see if the is any compatibility between Stanley Fatmax V20 power tools and DeWALT power tools.