This alarm appears due to the "Home Position" lost because of battery voltage drop for axis encoders.
Normally when machine is on, the supply for encoder is given from drive, but if it is off for a long time, the battery in the drive is used to retain supply to encoder, hence the battery power is consumed.
There different procedures for recovering the home position depending upon the configuration from MTB. You need to tell the value of axis parameter #2049 (1 or 2 ...9) & the CNC control model (M64/M65/M70). Depending upon your feedback, we can send you the procedure.