Albuzz,
I have a one year old boat, batteries same age. Just lost one deep cycle of my 24v bank. I had been reading about lithiums myself, and asking a lot of questions. From what people in the business and others told me, I just couldn’t figure out the math. Everyone suggested the 50ah battery. I explained that i spider rig quite a bit in the spring and all said they would do me just fine. I researched the companies and ended up with Ionic 50ah batteries (which have Bluetooth). My first trip with them last Monday was impressive I have to say. 6 hours of fishing with some wind and the batteries were at 92% when we got off the water. I took a handicap buddy of mine and had to spot lock a lot to manage fish and equipment. I was very nervous about the 50ah being enough, but I’m at ease now knowing that I’m in good shape with these. 19’ aluminum bass boat with 80# 24v trolling motor. Boat catches a lot of wind. I hope this helps, I understand what you going through not wanting to spend this kind of money and making the wrong decision. Good luck!