Dual battery question

[goin camping]

Just picked up a truck and it came with dual batteries and a big knob under the hood that let's me pick. Battery 1, Battery 2, Both and off.

How does this system work? Should I turn it to both and forget it or?

 

[craig333]

Pretty much, yes. Unless you're going to do winching or some other use whereby you risk not having enough juice left to start the truck.

 

[1911]

When the engine is running, you want both connected so that they both get charged. When you are in camp and running a fridge, lights, radio, whatever without the engine running, you want them disconnected so that you're only draining the second battery and your primary battery remains fresh for starting the engine.

 

[Walker]

I fully agree with 1911.

 

[Melody]

If you hook up two batteries together and let them sit, they will kill each other.

When you start your rig, it's nice to have two fully charged batteries together, but not a dead one and a good one.

In camp, you want them separated so you don't kill your starter battery, unless push/bump starting is really easy.

When winching, you want both batteries hooked up and ideally the engine running...unless you are underwater.


there are various ways to isolate two batteries. You can use an isolator, which makes your alternator work harder. Or, you can use a big relay which doesn't place a drain on the alternator. If you are using a relay, there are many ways to wire it. You may wire is so the two batteries are on when the ignition is set to run and/or start. Or it wires so that you have to flip a switch to connect them. The switch can be wired to power all the time or power when the vehicle is set to run, accessory, etc.

If it were my vehicle, I would like to know exactly how it is wired.

 

[rb70383]

If you hook up two batteries together and let them sit, they will kill each other.

How so? My diesel has two batterys in parrallel/non isolated. No issues at all.

Now if your saying a dead battery and a good one hooked together, yes. One will try to charge the other one.

 

[4x4junkie]

If the batteries are of the same brand, type and age, there's usually no problem. If you hook a flooded battery together with an AGM type, or two very-different-age or brand batteries though, then you're much more likely to have issues.

I have two Voyager deep-cycle batteries connected in parallel on my rig. Been running them like this for decades. Typically I can get about 8-10 years of good use out of a pair.

 

[Pooch72]

Though this isn't an expedition setup, I run dual batteris in my Supra. The alternator runs into a battery isolator, and charges both batteries at once. However, the batteries are not linked together, and theoretically don't even know each other exists. One battery runs the engine and the car, the other battery runs the stereo system. If, however, I were to ever leave my lights on in a parking lot, I can actually jump myself with my other battery, and have actually done so (but I'll never admit it).

I plan to do the same setup with my truck one of these days as the setup in the car works as good as I could have hoped.