For most new models, the procedure is the same. Pushing down on the external handset button, slide the Volvo Cars cover up and away from the handset. This will reveal your skeleton key blade and another button that releases the back cover of the fob in a similar fashion. Once the back cover is removed, identify the fob's battery cover and twist counterclockwise to "open." The positive side of the battery is now revealed. Remove and replace with the correct battery and ensure the + symbol is facing you before you close. Reassembly is the reverse of removal. If the fob battery was to blame, this should rectify the issue without any additional programming. Earlier handsets are similar.