There are many options for mounting and wiring the fishfinder battery. It's got to stay dry, so if you kayak on a lake or bay, you can stick it in a waterproof box ranging from a Tupperware-type container to a Pelican case and stick it below deck.
Kayak anglers looking for a self-contained fishfinder and battery solution that can be easily mounted to any kayak with rails should consider the YakAttack CellBlok. Its smart, compact layout is one of the best solutions we have seen. The CellBlok will be available for purchase Monday January 27th 2014.