Replacement battery needed, For portable sonar

Exactly, they are not designed to draw huge amounts of power at once, which gasoline engines require to start. That's why none of the LifePo4 batteries have a CCA (Cold Cranking Amps) rating on them.

BUT now....
Dakota has "...12v 60Ah Dual Purpose 1000CCA Starter Battery Plus Deep Cycle Performance".

I do get your point that most don't, and the separation of "purpose built" batteries.

After reading the good information here, I realize that I keep a small Li-ion jump starter pack and a small 18V Li-ion power tool battery (to power the tire inflator I have in my emerg kit)...went to bring them in. Just hope I remember to take them with me when I go out...it can be a problem. In the summer at least, they are in a shallow storage area under the cargo space so they should stay much cooler than in the car itself. But we have had a "few" below -20oC nights so far this winter.