I have a f 350 super duty 4x4 1987 will adding another battery or 2 increase my cold cranking power? and i use extra lights on the back alot to see while loading and unloading! ive got a switch that has three settings on it.battery A,B and both , i was going to use that to run my lights and to back up my original batterys for cold starts or dead battery.is there any spiecal way that they need to be wired or is this too much for my altinator?sugestions and advise welcome ,thanks
You have the right idea and a good start to implementing it; more batteries are always better.
This is how I did my multiple battery setups in some of our trucks:
To maintain 12-volts, and not 24 or 36 or even more, always put the HOT cables on the +/positive posts and the GROUND cables on the -/negative posts and you will only ever have 12-volts, regardless of how many batteries you connect.
All of my batteries are Group 31s stud terminal.
I have two dedicated starting batteries that are only ever used when starting the engine; I have these tied together via a four position Cole-Hersee switch as you already described; I can turn ON both batteries, turn OFF both, or turn ON only a single battery should one or the other ever have a dead cell or internal short or such; I can also turn OFF the batteries as an anti-theft measure.
The alternator is always connected to these batteries.
The remaining batteries power ALL other accessories and are isolated from the starting batteries whenever the engine is not running by an oil-pressure switch controlled HUGE constant-duty solenoid.
When oil pressure reaches 5-psi, the solenoid engages and thus connects the accessory batteries to the alternator and starting batteries; when the oil pressure drops below 5-psi (engine OFF), the solenoid dis-engages and breaks the connection between the starting batteries and accessory batteries.
I have a big battery ON/OFF switch that can connect the accessory batteries to the starting battery circuit should I ever need to "self jump-start" the engine in the event that something should be amiss with the starting batteries. (or should the big solenoid ever fail)
I can leave lights and accessories ON for days and it not affect the starting batteries; they will remain fully charged and ready for action, regardless of how low the accessory batteries may become.
This constant duty solenoid set-up is way better than the more commonly used isolaters as I have a lot more control over what is going on with the batteries and a lot more options as to the what and when.
I hope this helps.