I just put a 24V TM on a small boat I have in place of a 12V. The boat came with a 2 bank charger on it. My question is can I use a 2 bank to charge both TM batteries and let the motor take care of the starting battery. I'm just not sure if both banks are deep cycle chargers.

Yes they both SHOULD be able to charge deep cycle batteries, never seen it any other way. What kind of charger is it?

How big is your motor? Do you run it allot to keep the battery charged?

Yes the onboard will charge both TM batteries. From personal experience when fishing long hours with not to many long runs your cranking battery  may need a shot of charge.

Happened to me a few times on week long fishing trips. Either charge the cranking battery every two days or so or carry jumper cables.

I've always had three batteries with a 2 bank charger. I use a portable charger for the cranking battery. The charger went bad last fall so I now have a 3 bank. Much more convenient.

Unless you do a lot of running, the motor will not keep the cranking battery fully charged.   It should be charged when you come in at the end of the day.   The onboard charger should be keeping your TM batteries maintain if you are leaving it on 24/7.  The cranking battery will need to be charged every month or a battery maintained connected to it.

Yes the onboard will charge both TM batteries. From personal experience when fishing long hours with not to many long runs your cranking battery may need a shot of charge.

Happened to me a few times on week long fishing trips. Either charge the cranking battery every two days or so or carry jumper cables.

Been there, done that, last year.  Didn't have jumpers.  Thank goodness wing nuts were used for all the connections.  Connected to a trolling motor battery, started up, and back to the ramp.

Got the jumpers from my truck, switched the batteries back.  Jumped the starter battery to a tm battery, and started it up.  Ran around for a half hour or so to charge up the starting battery.

The two bank charger does the two trolling motor batteries.  A couple of times a month, I hook up my portable charger to the battery, and bring it up to snuff.

With my last boat I had that problem so I put a 3 bank charger on it & the problem went away. I use the T/M way more than the engine. With all the acc. coming off the starting battery it's a good idea to charge it after a day on the water.