Lithium battery for on board fish finder question

[kickingfrog]

Mad money this year is for new batteries for the boat. I'm sold on lithiums for the trolling motor and from the other thread know what I need for my setup. However the information on what I should use for a dedicated battery for the fish finder seems to be a bit more murky. I've got a Garmin ECHOmap CHIRP 95sv. It has down and side imaging. I do fish full days so I want 8-10 hours of use but don't think I need multiple days as I can recharge overnight. I want as much battery as I need but don't think a 12v 100ah is necessary for my finder so the question is: Is 30ah enough or just go 50?

[smitty55]

More is better I would think. Better too much than barely enough, it will keep the battery from getting too far discharged. It's never good to let any battery get completely drained. Plus you never know if you will go on a weekend camping trip where recharging won't be an option.

[Fisherman]

Simple way to calculate is using the mfgrs power consumption info X 12 hours per day for one days use.  If you're going for a couple days, double it.  Double that and it's unlikely you will ever drop the battery below 50% and make it live longer.