Here's my current set-up on my boat:

I have 2 deep cycle batteries (sorry, but I can't remember what size they are...haven't had to mess with them at all in the 2 years I have owned the boat) and 1 starting battery. I only have my 24v trolling motor (Motorguide Tour 70) hooked up to the deep cycle batteries. I have my big motor ( Merc 175 EFI), bilge pump, livewell pump (very rarely use), bow depth finder (older Lowrance unit), and console depth finder (Humminbird Helix 9 Mega) running off of the starting battery.

A typical fishing day for me consists of using the trolling motor pretty consistently, but generally at low (10-30%) speeds, with the occasional use at higher speeds to move from one area to another if I don't want to start the big motor to go a few hundred yards or less. I'm generally not on the water for more than six hours at a time, and I only get out to go fishing an average of once a week.

I'm looking at the possibility of going with Lithium Ion batteries, but based on my set-up and my needs, and the cost associated with Lithium Ion batteries, I'm not sure if it would be a good idea or if I should just stick with lead-acid batteries. So I'd appreciate any input or recommendations as well as answers to the following questions:

1. Can I even use a Lithium Ion battery for starting my big motor? I've read that I shouldn't use an AGM battery or a deep cycle battery for starting my big motor because of something to do with the stator. If I had to keep a starting battery just for the big motor, it wouldn't be that big of a deal, but if I could use the Lithium Ion's it would be best.

2. I've read that the Lithium Ion batteries are good for thousands of cycles. Considering that I only get out and fish an average of once a week for six months a year where I live, that would equate to the batteries effectively lasting me the rest of my fishing life (30+ years). What is the life expectancy of these batteries assuming I only charge them 20-30 times a year?

3. What amp hour size would you recommend based off of my electrical equipment, time on the water, and use? Would I be able to get away with something lower than 50ah per 12v battery, or would 50ah be the lowest recommendation?

Any help would be greatly appreciated. Thanks!