Dual Battery Questions

Chips

Mothertrucker
Hi, I'm a newbie here. I've just bought a 2004 Suburban Z71 to which I'm planning on making a few mods to turn it into a camper of sorts for my girlfriend and I. What I'm stuck on is the electrical stuff. I've read quite a few threads on here now but I'm struggling to put all the different parts of the system together in my head, and I'm not sure what I'll need to meet my power requirements.

What I want is a dual battery system that charges both batteries off the alternator. When camping I want to be using the secondary battery only so I don't discharge the vehicle battery, but I still want to be able to use some of the vehicle systems including internal lighting (using LED bulbs), stereo and DVD player. I'll also need to run a 12v cooler and be able to charge my laptop. When the engine is running I still want all that stuff to work.

So I guess what I'm looking for is a dual battery system that will power all vehicle and secondary systems all the time. It needs to be switchable between the two batteries so I don't discharge the vehicle battery, and both batteries need to be charged off the alternator. Now I'm guessing that these are fairly simple requirements but I just haven't found any info from someone with that exact setup. Can anyone help point me in the right direction?

Bonus question! What would it take to add solar to the secondary battery? The solar panel would need to be removable for when the vehicle is being used purely as a daily driver.
 

robgendreau

Explorer
Generally people use an isolator between vehicle battery and the house battery, so you can run all the camping stuff independent of the vehicle electrical.

But there are battery bank switches, available at any marine or RV place, that will allow you to do that manually.

But in a standard configuration with an alternator, the house battery and stuff attached to it is powered by the alternator, in essence. Charging the battery, cooling the fridge, etc. So when the engine is running all that works.

In that setup, you can still turn on anything that runs off your vehicle battery. Just use the ACC on the ignition switch. And generally, most vehicle cig lighter receptacles are always hot. The dome lights work too. Just like things are right now in your vehicle, before adding anything.

You seem to want to combine the starter battery and house battery for that stuff, but that's generally not ideal. They are different kinds of battery. If you have something that sometimes you wanna run off the vehicle power circuit, and sometimes off the house battery, wire it that way. Or keep it simple, and just plug the device into the house battery 12v receptacle instead of the vehicle's. You could also run wiring from the house circuit to your stereo system.

One reason for this is that one battery can parasitize the other. Even if you had nothing "on," a low house battery is going to affect your vehicle battery, with possible adverse consequences. So you would need to keep on top of it. But in some cases you might WANT that, to add to the power to start. It's pretty common on boats, and that's when people use a manual switch, which might have both in use, both off or either one on.
 

daddyusmaximus

Explorer
I had a switch that I would manually have to turn on for my old truck to charge the house battery that powered the extras. I would charge while driving. I used a constant duty high amp solenoid I got at an RV dealer. I'm going to duplicate it in my new Jeep. I like simple things I can control. In theory, if I ran the vehicle battery low somehow, I could jump start it with the house battery if it was charged. Never had to try.
 

rruff

Explorer
What I want is a dual battery system that charges both batteries off the alternator. When camping I want to be using the secondary battery only so I don't discharge the vehicle battery, but I still want to be able to use some of the vehicle systems including internal lighting (using LED bulbs), stereo and DVD player. I'll also need to run a 12v cooler and be able to charge my laptop. When the engine is running I still want all that stuff to work.

I'd get a pair decent sized deep cycle batteries and use them for everything. Ditch the starting battery. No isolators needed. Lead acid batteries shouldn't be discharged more than 50% anyway, and if you screw up and drain them to 20% they will still start your vehicle. Keeping an emergency jumper just in case.

The 12v cooler is going to suck enough juice that you will want solar if you park long (more than one night). Just get a portable 100W or so that plugs into the lighter and folds up.
 

Chips

Mothertrucker
Thanks for the replies, folks.

To simplify the question a bit (hopefully) I won't be adding any additional outlets, I just want to use the 12v outlets already available on the vehicle. I've counted 3 so far which will be enough, but there may be more. So essentially what I want is just a secondary battery to run the vehicle electrical system while the engine is off so I don't drain the primary battery for starting. Both batteries need to charge from the alternator when the engine is running.

I was looking at the $50 isolated dual battery thread. Would the first solution meet my needs with a solar panel hooked up to the secondary battery to keep things ticking over while parked for a couple of days?
 

rruff

Explorer
Think about it. If you have two deep cycles instead of starter and deep cycle, you have doubled your deep cycle capacity and simplified charging. What's the downside?
 

Pauluminous

New member
In this case I would do it the other way around. Since your acc. are already wired up and you don't plan on adding anything (probably), just use that and keep a secondary battery isolated just for starting. A manual switch would be the easiest. You'll need a key in the ignition and turned to acc. though.
Or just get a decent booster pack, charge it while driving and use the next morning if/when needed.
 

Ducky's Dad

Explorer
In this case I would do it the other way around. Since your acc. are already wired up and you don't plan on adding anything (probably), just use that and keep a secondary battery isolated just for starting. A manual switch would be the easiest. You'll need a key in the ignition and turned to acc. though.
The solution may even be simpler than that. With a pair of decent AGM dual purpose batteries, you can run everything off the main battery and then start the truck on the second battery. Just install a simple isolator switch (like a Blue Sea or Marinco) between the batteries so that you don't drain both while parked, and then switch in the second battery for starting and driving. The only time you really need to isolate them is when parked and using accessories. If your accessory outlets are always hot, then there is really no additional wiring required. Don't know about your Sub, but lots of GM SUVs have a hot socket back by the tailgate for this kind of stuff. If so, you don't even need to turn the key to ACC to run a fridge.
 

Chips

Mothertrucker
That's correct. I have 3 always hot outlets. Two up front and one at the rear. So I can run my cooler or whatever and the internal lighting without the key in the ignition at all.

I think I'm getting to grips with it now. I like the reversed idea, with the starter battery isolated until the key is turned. Then as long as the engine is running I would get a charge to both batteries.

So all I would need to do is add a 'house' battery and a solenoid which would be powered when the key is turned to connect the vehicle battery.
 

Chips

Mothertrucker
WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator

Use this and hook the house battery up to a fuse panel and hook all of your accessories up to it and you are done. It doesn't care if the house battery is deep cycle or not. Have had this in my truck/camper combo for 3 years with not problems.

So I could just use another car battery with it?
 

Ducky's Dad

Explorer
So all I would need to do is add a 'house' battery and a solenoid which would be powered when the key is turned to connect the vehicle battery.
Technically, you don't even need a solenoid. I have a Painless Performance solenoid isolator in my truck and it is very convenient to switch things from a toggle on the dash, but a rotary switch under the hood is simpler and cheaper. AGM dual purpose batteries are the way to go because they are good for starting and for running accessories. If your Sub does not have dual air conditioning, you should already have an extra battery tray behind the headlight, opposite the factory battery. Use the biggest battery that you can fit, probably a 34/78, but you may be able to fit something like a Grp 65.
 

Martinjmpr

Wiffleball Batter
Technically, you don't even need a solenoid. I have a Painless Performance solenoid isolator in my truck and it is very convenient to switch things from a toggle on the dash, but a rotary switch under the hood is simpler and cheaper. AGM dual purpose batteries are the way to go because they are good for starting and for running accessories. If your Sub does not have dual air conditioning, you should already have an extra battery tray behind the headlight, opposite the factory battery. Use the biggest battery that you can fit, probably a 34/78, but you may be able to fit something like a Grp 65.
.
On the GMT-800 trucks the extra battery tray is on the passenger side by the firewall. The battery behind the driver's headlight is the main battery. I think it was on the GMT-900 trucks that they switched places and put the main battery by the firewall on the passenger side and the aux battery behind the driver's headlight. ;)
 

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