Spent a good 10 hours on the water Thursday with no issues. Charged the batteries as soon as I got home. Wasn't fully charged when I took off for the lake the next morning and the batteries pooped out on me after about 7 hours and had to get jumped. Cranking and the 2 accessory batteries. Batteries are about 3 years old so I'll be replacing them soon BUT was wondering if going from a 2 bank to a 3 bank would eleviate that issue going forward?...

Also be upgrading to most likely a 36 volt TM in the coming months if that makes a difference.

Each battery should be fully charged before going out on the water. Get a charger that will charge all of your batteries at once. The higher amperage chargers will charge your batteries quicker.

When you replace your batteries, get the biggest you can afford and you might want to take a look at agm style batteries. The have a lower discharge rate and higher charge retention over lead acid batteries.

Also if you get a 36 volt tm system it will be easier on the batteries than a 24v setup. The 36v system is more efficient. If you plan to get a 36v system soon, get a 4 bank battery charger

4 bank? I may stick with 24v and bump up to 80 pounds in that case. Save a little coin and the current 70lb TM does a pretty good job even in windy conditions. 80lb should be a nice improvement.

I heard about dudes using tractor batteries as their cranking battery?...

Each battery onboard should have its own changing bank. 3 batteries = 3 banks or 4 batteries = 4 banks. Using a built-in charger like Minn Kota's 460 will do a great job or keeping the batteries charged as well as maintaining. I leave mine connected every day.

Get a tm that is digital. All new 80lb tm will be digital. Get a 3 bank charger to charge all the batteries and get you some agm style batteries. You should be good to go with that setup. When selecting batteries, get at least a size 27 or larger

Ok. So, the boat I bought has a 3 batteries but a 2 bank charger. I figured that the cranking battery doesn't necessarily require a charge and that the 2 banks just charges the DC batteries. Not sufficient enough?

Go 3 bank

Correct,all 3 batteries need to be charged. In the short term,put another charger on the cranker.

Before you put an AGM cranking battery on, what motor are you running? If you have a stator/voltage regulator type charge system an AGM battery can be a costly mistake. AGM's take charge slower & it can fryout a voltage regulator/stator & actually cause an engine fire. If you're running a newer motor with an alternator style charging system you'll be ok with AGM battery.
For plug in charging
3 batteries = 3 bank charger
4 batteries =4 bank charger

Agm batteries actually charge quicker than lead acid batteries.

I'm running a Merc 150 Pro XS Optimax

You can get a lead acid battery or a agm for that motor. You wont have issues running either. Make sure you get one with at least 750 cca

Roger that! I've seen those Optima blue top batteries around. Are they worth the extra few bucks? Otherwise, I work for Costco and we sell Interstate marine batteries for a reasonable price.

You're good to go. If you work at Costco by all means get those batteries. I check electrolyte level in mine on a monthly basis, remove & clean all terminal connections, use nut (not wing-nuts) on terminal posts. I plug mine in as soon as I get in from fishing & leave them plugged in as my charger goes into maintenance mode after charge is full. I run a 94'Merc 200 Xri (stator/voltage regulator) with a (cranking) 31 class wet cell lead acid battery that runs all electronic graphs, aerators, bilge, & lights. I ALSO carry a Weego emergency battery jumper( small & about $100).

For Minnkota Fortrex 80# 24V Trolling motor=batteries are 2 Exide 31 class AGMS with 1110 cranking amps,& 200 reserve minutes, i never have ran out of juice even on all day high wind days. I get at least 4 years service out of mine usually. Im happy with that.
It all turns into the Chevy/Ford/Dodge debate when battery choices are asked about. These Exides would be a great choice for your application all the way around.
Look for the highest reserve capacity minutes for TM, buy what you can afford & fish as much as you can.

I used a small portable charger for my cranking battery. Most of the portables offer the same features as an onboard these days as far as maintaining and charging.

My .02 worth, or this information and a buck will get you a cup of coffee in some places.
Do not get AGMs for the trolling motor. AGMs usually have a lower RC than lead acids of the same group size. RC is the ability the battery has to hold a charge over a given period. The AGMs will make you think they're holding a charge because they are made to deliver the power throughout their discharge cycle. Problem is, when they die, without warning, they're dead and have to have another battery (slave battery) to jump in parallel before they can be recharged (once they're discharged). Also, you have to make sure your charger is AGM compatable or it will burn the battery while trying to charge it. Now, for the cranking, a 31 series AGM is good. This is because it does deliver the power througout the discharge cycle, but with pumps, electronics, and outboard you shouldn't discharge it to the point of a trolling motor battery. The alternator of the outboard will keep it up while you're running, and will just need a "top off" needed when you connect the charger.

Agms will let you know they are dropping in charge throughout the day. They will not die without warning. Lithium batteries will die without warning because they are designed to work at full capacity until dead.

You don't have to buy a 3 bank if you already have a 2 bank. You can buy a single bank and add also. I now have 4 batteries and I had a two back so I just bought a used 2 bank and run them both. I just use Walmart and interstate batteries with no problems. Battery size mattress and a digital trolling motor really helps. I could go two days without charging with a 80# tm if I needed to.

A 70-80 won't be that noticeable but the digital maximizer will.