DEVO12S Error " CRITICAL BATTERY LEVEL DETECTED"

Hi together

I run a DEVO12S since 2 years without any problems but 2 weeks ago the trouble came over me.

One day in the past I used it several times and suddenly after switch on an error display appeared.

“CRITICAL BATTERY LEVEL DETECTED” and all calibration data of the touchpad and the sticks and the time are gone.

I checked the backup battery and found only 2,8 V .
I changed it but the problem persists.

Is there a special handling necessary to reset the controller (or something else) after a battery change?

Regards
Achim