Rewiring and separating Electronics from starting battery.

I decided to isolate my Lowrance Hds 16 and my 9in Garmin electronics and power them with a lithium battery. That was the easy part. Now that i have begun to rewire, I am asking myself if the NMEA network must be powered by the lithium battery to be seen by the lowrance and Garmin. I don't want to give up the info the engine gauges from the NMEA network provides or can NMEA remain on the AGM circuit.

It seems logical the NMEA could remain on the AGM starting battery network but I need expert advice.

It's possible the NMEA needs to be on a common ground with the rest. Only one way to find out.....wire units up, leave N2K on AGM and then look in the device list to see if the network shows up.

Split the NMEA backbone.......May need to add a simple and inexpensive NMEA power isolator and introduce another power node coming from the new Lithium Ion battery on the Lowarnce/garmin side of the isolator.