Probably not using a deep cycle battery in a kayak. That's one reason. I have a deep cycle battery and I can run a live well aerator, lights, 2 other sonar units, aerator on a timer switch (on 1min. every 7mins) and I can charge my phone off of that one battery over a 6-8hr period and my battery may have 80% charge remaining.

Its a heavy battery weight wise because its a deep cycle marine battery.

These units were not designed for kayaks although they can be applied to one.