Battery balancing

[ufoDziner]

I'm swapping out my bad 400A generator for an alternator. When doing this, I'm going to add a 24V-12V DC/DC convertor to run the stereo I plan on installing, etc... The plan is to run the 12V transmission power from from the stepdown converter as well. From what I can tell, there is no system in place for battery balancing. While they really shouldn't get too far out when using a converter, I'm curious if anyone runs a battery balancer to ensure the batteries are matched, and if so, which one do you use. Thanks.

 

[ufoDziner]

With this swap I'll need to update the wiring a touch. There are three wires with yellow ends (pic attached) that appear to be for the 12V side of things. I'm new to the manual system with these, so if someone could direct me to the manual and section as to where it shows what these wires connect to, I'd very much appreciate it. Additionally, there is this unit bolted to the side (in second pic, circled in blue) that I can't identify. Again, any help is welcomed. Thanks.