Im getting started in yak fishing and was wondering what battery everyone is using on their yaks?

i use the nocqua battery for my fish finder

My comments are based on assuming you're referring to a fish finder battery. I highly recommend going with lithium if you can swing it. What size depends on your FF and the amperage draw. I use a FPV 17.5 AH lithium battery it's pricey tho. I don't need that much for my FF but I do have lights and USB outlet I run off that same battery. Nocqua offers a 4.4 ah and a 10 ah lithium battery. If you think 6 ah will be enough here's a budget lithium battery that can be charged with a standard 12v battery charger.
https://www.amazon.com/gp/product/B07Q7FY8CC/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

I work in a hobby shop and I have some 22,000 mah lipo batteries. Would that be suitable?

I use the Nocqua 10AH battery. I like it because it has a lot of power in a small/light package. I hang it off the bottom of the seat with a gear tie so not having to run cables far or put any hole in kayak for them. I have the Lowrance Elite 7 TI finder with triple shot transducer and that is all I hook up to the battery.
Specs say can draw up to 2 amps. I can be out over 8 hours on a charge, longer if some of the time is at night when I turn the brightness down.

If I understand what you're saying I think it can be done. I'm not sure exactly how tho. If you know how to assemble the batteries and plates so it's configured to produce 12 volts with at least 6 ah then it should work. I believe you would need a battery protection board to prevent overcharging and explosion/fire and some type of housing to put it in and battery terminals. I'm guessing you can buy the Miady 6 ah battery on Amazon cheaper than you can build one.

I have the same FPV battery and it’s been great. It’s expensive, but I plan on using it for a long time.

I am using a YakAttack CellBlok and i attached their Switchblade arm and Fish Finder mount LocNLoad setup. I then put a Dakota Lithium 10Ah battery in the CellBLok.

Now I can loosen the two screws on the CellBlok and slide everything off in one piece and take it in the house to charge or keep out out the weather when not on the water.