The reason why you are unable to view the battery voltage is because you may have send a command to turn the shore power on, because of this the Yacht Sentinel now will only monitor the shore power. Currently the Yacht Sentinel can only monitor either the battery voltage or the shore power at one time.

To switch back to monitor the battery voltage all you need to do is enter:
Your password, BATT=12/24.

If you have a default password of 4444 and you want to set your voltage to 12 you would enter;
4444,BATT=12

Since the Yacht Sentinel cannot connect to boat voltage and the shore power at the same time to switch back over to
monitor the shore power all you need to do enter the command
4444,BATT=SP
Another way to do this is to go into the power/battery settings in the application and to select SP
to set the shore power ON