That may be true ... but, my current Hook 7 & my former E5DSI units both were hooked into the trolling battery wiring & the only problem I ever had was when the battery got low the units would just shut off. There was still a little juice left in the battery to use the trolling motor, but very weak thrust. Never had any "interference" on the units when using the trolling motor. I'm thinking that his 80ah Lithium may get sucked dry from the LS setup plus the trolling motor, a lot sooner than he might want (or expect).
All I know is ... if my 50ah Lithium battery, fully charged, doesn't run my LS setup much longer than 6-7hrs ... then I'm gonna be buying a 100ah Lithium for it. Even at 22lbs, it's MUCH lighter than the 68ah AGM (45lbs) that I originally bought for the setup (& is now my trolling motor battery).