Holy Cow Dave!
I just got into the low end entry model kayak last year but that's the wildest kayak rigging I've seen! I used to have a 55 lb V Drive on my Nitro and I'll bet it'll move that kayak close to 10 mph, or more? That seat, cooler and full size battery are impressive!
I put a Lowrance Hook 4 on my kayak this weekend and bought a Li-ion battery $19 from Amazon (was $19.52 when I bought it, says $24.99 today - don't ya love how they do that pricing gimmick?).
Anyway, I measured the Hook 4 at full brightness and it drew about 300 mA. This battery should last over 10 hours. And the impressive thing is it's only 6 ounces. If it lasts I may try it on the ice too, heckuva lot lighter!
Hope to see you out there. Now I know what to look for (son's yak).
Thanks for showing us the way!