One of the hardest choices for me was what battery to use with my kayak and fish finder...there are a couple common choices, either Seal Lead Acid types or Lithium Ion. Both have some advantages and disadvantages. I ended up going with a Nocqua Pro Power Kit 10Ah lithium Ion battery...it is small, light, and easy to use.
One major question I had was how long would my battery actually last as far as powering my fish finder, so I hooked up my camera to find out.
It was way longer than I expected, even with max brightness and the transducer attached. I timed how long it took to take my Garmin Striker 4 down to 10V which is the minimum recommended voltage.
It ended up running for 36 hours non stop before voltage dropped to 10V...pretty impressive IMO.