Electric-Only boat setup

My winter project is setting up my boat for electric only lakes. Right now my setup includes a transom and bow mount motor that has a battery dedicated for each. For the fish finder, nav lights and bilge I'm thinking of adding a third, smaller battery just for the electronics. Wondering if anyone has a setup like this and if so, what size battery do you use for this? I'm thinking that the battery does not have to be as large as the ones for my trolling motors so maybe a motorcycle battery? Something else?

Any and all suggestions welcome!

While I still have my outboard on, I have a bow and transom mount trolling motors that share one battery, and my electronics are all on a 17ah battery. Never had any trouble, and often I find that I never crank the outboard.

I have a wheelchair battery (AGM) that I bought for powering a trolling motor. It is compact, but has much better capacity than a motorcycle battery. Still use it in my jetjon. FWIW

I plan to make my 12ft jon boat a electric only due to the fact i'll use it primarily on small lakes and ponds that only have a 5mph speed limit on the water so I plan to run at least 2 deep cycle marine batteries and for my electronics I plan to run a battery jumper that you use on cars ect I already have one and I rarely use it so its kind of a waste to let it just sit and rot the 2 batteries will run the trolling motor I plan to put a switch from one battery to the other so when the one battery dies I can ake it back to the dock