How Do I Run Dual Batteries?

[happytrails]

hey guys, how do i go about running dual batteries?

[fourwd1]

Once you figure out where you want to mount them, you'll need something to hook them together. You can't just wire them together, they need to be isolated from each other when the engine is off to prevent a charge/discharge cycle between them.

There are 3 choices, a switch, a solenoid (relay), or an isolator.
A switch would be like one used in a RV, having multiple positions (A, B, A+B, OFF).
A solenoid automatically connects them when the key is ON and isolates them when it's off. Just be sure to get a continuous duty rated solenoid, a normal starter solenoid won't cut it.
An isolator is the easiest to use, just connect batt A, batt B, and alt, but it does create a small voltage drop (full alt voltage does not reach the batt, so may create a charging issue on some systems).

[BigDaddy]

I am running duals and use a solenoid that will open when I have my Key on. It is the same as the RV type, I picked it up at a place that sales Snow plows and tool boxes for the back of trucks, it was right around $20.00. I went to Checkers and picked up a plastic battery box and put my Yellow top in the cab. Works out good when we need to weld, a strap and few bolts and we are good to go!

[keyice]

Okay the proper way to run dual batteries is different for most people, they still must be hooked in paralell mean + to +, - to -.
+ to -, + to - is called series and will add 12v +12v to a total system voltage of 24v, this will fry most car systems.
Some people like to run isolators to keep one battery from getting drained by a winch or lights. You don't have to do that if you don't want the only problem is if you winch a dead stick aka the truck won't start to charge the batteries when you get to the top of the hill you won't have juice to start it. The disadvantage to isolators is it limits the draw on the second battery to 90 amps meaning you can only pull one battery plus 90 amps
so who cares right, well most winches at max load will pull 450 amps continuously so if you battery is rated 800 cold cranking amps, you won't be able to winch very long.
I would recommend hooking straight + to +, - to - so you can draw evenly off 2 batteries, and keep a good set of at least 4 gauge wire jumper cables in you truck so if you winch to both batteries end you can use your unbroke buddies truck to start it. after you out of your mess.