Trolling and fish finder battery

[southernbass]

I have a pontoon that I'm looking to get a battery (fairly cheap as possible) to power a trolling motor and a fish finder. So my question is where is a good place to go and what's a good size to go with that I can use that won't die after just a few hrs of using? Thanks for the help.in adding a pic of my toon and I haven't got a motor yet for it seeing I'm still trying to figure out what size I should go with
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