Monitor ignition back-up battery voltage

[albery]

I have a dual electronic ignition with an emergency back-up battery.

I would like to be able to monitor the voltage status during pre-flight checks while switching briefly to the emergency setting during power checks.

It seems the only way to do this is to connect to the Auxiliary bus 2 or 3 input, but that would mean that the EFIS would power itself from that connection in the event of alternator failure.

I need to ensure that the back-up battery can only power the ignition and not the EFIS.

Is there a practical way of achieving this?

[GRT_Jeff]

The HX has 8 Analog Inputs that you can use to read and display voltages. The settings are in SET MENU, General Setup, after the serial ports. If you configure one of the inputs to the "Aux (EIS compatible)" function, set the Scale Factor to 25, set the Offset to 0, set the Integer/Decimal mode to Decimal, and set the Aux Function to Aux, the input will read a voltage to one tenth. You can give it a label and set alarm limits if desired. Then pick a data box or bar graph to display it on.