If the battery is showing 27 volts then it must be working. Something else is wrong. To confirm, remove the battery connector wires and then check the battery voltage.
The squealing could be a hung up motor. If possible with the cover off, Blade removed!!!!!, The bot sitting on blocks so it can't go anywhere, try removing the motor connector to one motor at a time.
While you have the connector off the motor, check the voltage at the connector.
Check for a fuse that may have blown.