There are no specific measurements for mounting the charging station of the Dyson V11 Extra in the sources provided, but in general we can derive some general guidelines.

Typically, Dyson vacuum charging stations require a flat surface large enough to accommodate the station and the vacuum itself. Here are some general dimensions that often apply to such stations:

- Width: Approx. 15-20 cm
- Height: Approx. 10-15 cm

Your available space of 16.5 x 55 cm should therefore be sufficient to mount the charging station of the Dyson V11 Extra. However, it is advisable to check the specific dimensions in the operating instructions or on the packaging of the charging station to ensure that the installation can be carried out without any problems.