Ducati MULTISTRADA 1200S ABS 2015 Workshop Manual page 401

Replacing the battery in the active key
Note
The keys do not need to be reprogrammed after replacing the battery.
Remove the metal part of the battery.
Remove the rear plastic shell of the grip by pushing it forward and lifting it as shown in the figures.
After separating the plastic shells, remove the battery protection sheath (2).
Remove battery (3) and install a new one.
Install the battery in place, paying attention to respect polarity: positive pole (+) must be facing up.
Important
Only use the required type of battery.
Refit protection sheath (2) on the battery.