help wiring new boat

I am running a 12 volt power drive with an i-pilot on dual batteries, I would like to put my 768 up front and a 798 on the helm with an inter link. Now on to the questions can i wire both units to the trolling batteries or should I run them off the cranking battery? On that type of set up do u run both units off one gps receiver or a receiver for each unit. I was thinking if everything ran off the trolling batts I could leave both units on all day and not worry about having enough juice to crank the big motor. Does anyone see any problems with that set up, if so how would you guys rig it?

Running off the TM batteries is asking for interference. Most everybody runs off the cranking battery. The units use a very small amount of power.

Some people share a GPS and some want the precision from having the GPS close to the transducer.

seperate antennas on hummingbirds ,means better accuracy

Plus everytime you step on the go button of the troller you have a major surge of electricity. Electronics do not like surges.

Thank for the help, I knew u guys would have the answers I was needing!