I have a dedicated LiTime 50 Amp that runs only the LVS 34 with 12 inch screen. I can run it all day, for multiple days in a row, with no degrading on signal or display. I would have to say a 100 amp would be overkill. I run seperately the rest of my boats electronics on another LiTime 50 Amp lithium. I have had no problems.

A Garmin 12" graph and a LVS 34 will draw a little over 4 amps so max run time will be 10-12 hours on a 50a battery. Must be short trips if getting multiple days off one charge.

Your estimate is spot on, I should have stated my trips are between 4hrs to 6 hrs. Thank you for clarifying that. I charge every 3 trips or so.

That brings a great point up, for the OP, the trip time would determine battery size. I was fine with a 50A, i can easily charge at home, and I never am close to running empty with trips at the most 6 hrs

Correct, you can get more by turning your screen down, powering down when you aren't using the graph etc. The black box uses nothing to speak of, the 12 inch screen on 100 percent gobbles power.

If the sun isn't too bright you can turn them down from max to about 6 or 7 and almost cut amp draw in half. I run three 12's and a 15 and it makes a huge difference doing this.

I run black box, lvs34, garmin 106sv off of a LiTime 12v 50ah in my right rod locker. So far, I have had no issues with power or my graph dying. I do watch voltage drop throughout the day but it does not affect the picture. (atleast to my knowledge) Charge up overnight and get back after it the next day.

Mega Live 2 and Xplore 12.

I run them to a designated 16 volt lithium (52 AH) with nothing else. Does it make a huge difference? Who knows. I definitely don't lose picture quality over the course of a long fishing day.