I can't unlock the motors on cx-20 after firmware update. Have tried hints and tips but nothing seems to work

Preflight in planner shows battery voltage at zero when it’s fully charged. Any ideas anyone??

Some details would be helpful.
What board are you running?
What firmware?
What battery monitor?
What pins have you set as the battery monitor pins?
What GCS?
Planner could mean Mission Planner or APM Planner and on what platform?
Have you done the calibration in “Planner”?