Hmmmm, Iv never used one, but a deep drop reel under load would pull some amps, that looks like it says 4.2A max which isnt much, and not much capacity (14AH). I just looked up the Tanacom specs, 3A draw with no load, 10A stall and max current draw is 30A. You could ling a few of them in parallel to up the current delivery and capacity, but Id be lookin at using a glass matt (AGM) marine battery like a blue top optima (same as yellow top, just stainless posts). The higher the AH rating, the longer the use youll get, and the optimas (and some deepcycle batteries) dont suffer from being repeatedly discharged heavily (<11v). I assume you will be able to charge via the outboard's charging system anyhow. Just my two bobs worth....

 Nowhere enough cca's I reckon.

The battery you have attached would be more suitable to run your sounder or some other basic electrical device for the day. An electric reel will simply need to draw way more current than what these contain.

 Ok cheers boys, I'll take the deep cell one then, don't want to get caught out