Dual Battery Setup (Problem)

I've got a 2010 Sunsport with a dual battery setup. Battery 1 is a Marine Cranking Battery, and Battery 2 is a Deep Cell. I've been having problems with the charge in Battery 2 running out, and causing my electronics on the boat to do funny things.

Ive got selector switch set to one. I think my wiring is set up properly. Theres a small gauged wire coming out of the voltage relay, and i'm not sure what battery that is to connect to.

Theres also a medium gauged cable that looks to be coming from the floor (not the larger termanal cable). This is attached to Battery 2. I'm not sre if this is attached correctly?
All I have running to Battery on is the Positive coming from the switch. the Negitive from the engine, and the Negitive that runs parallel to Battery 2.

Any suggestions or comments would be appreciated.

Depending on your setup, you may have to change the dial to battery 2 to charge it.
I would try that. Also if you get a multimeter, you could read the voltage and see if it is getting charged with the boat running and the battery switch to 1. (I would think it should read around 14V).

If you hook a battery charger to the battery on 2 directly, does it hold a charge? (Battery could be getting bad and needing replaced.).

Yeah I'm thinking you just need to put your switch on 2 or All so that the battery gets a charge from the boat.

I trickle charged the accessory battery the other night and set the selector switch to charge both battery's at the same time. It seems to be working for now. Thanks for the comments.