The controller battery is worn out and needs replacement. As replacement is somewhat troublesome, we recommend that you request a service engineer to make the replacement and re-establish options and parameter settings. 

We strongly recommend preventive service on the other units at the same time to avoid further downtime.

If the unit can be taken out and returned to a DEIF service center then we can repair the unit, just note that a backup of these units must made before powering them down.

If it's not possible to send in the unit, or get a service engineer out to do the change. You can follow the battery change guide in the attached manual here. (6.4 Battery replacement) from page 24.