Ducati Monster 821 Owner's Manual page 202

Note
When the motorcycle is left unused
(approximately for more than 30 days) we
recommend owners to use the Ducati battery charge
maintainer (Battery maintenance kit part no.
69924601A - various countries; Battery maintainer kit
part no. 69924601AX - for Japan, China and Australia
only) since its electronics monitors the battery
voltage and features a maximum charge current of
1.5 Ah. Connect the maintainer to the diagnostics
socket located in the rear side of the motorcycle.
Note
Using charge maintainers not approved by
Ducati could damage the electric system; motorcycle
warranty does not cover the battery if damaged due
to failure to comply with the above indications, since
it is considered as wrong maintenance.
201