Simple Dual Batteries Questions

Hello all, I have been reading this forum for a long time and it has helped me with a lot of work on my 92 XJ, first off Thanks for all the help! I am about to do a dual battery setup in my XJ and want y'all to take a look at my plans and let me know what you guys think. First off I do a lot of remote camping out of the jeep and am doing this more for the extra battery and self jumping ability than for reserve capacity. I plan on using 2 1000CA red top Optima's. I plan on having both batteries on a large relay/contactor (250A cont./600A momentary) and both contactors tie into the jeeps electrical system where the factory battery does. I would run a switch in the cab for each contactor. (BAT 1/BAT 2) I thought of doing this for a few reasons 1: I will have full control of what battery is being charged/used at any given time. ( I will be adding a 3 position switch to a digital volt meter for bat1/off/bat2 so I can check state of charge between the batteries with one volt meter.) 2: I could completely isolate battery two when fully charged to provide emergency jump power. 3: This seems like a very simple set up that only has two components to fail and if need be one contactor can be bypassed in an emergency. I plan on upgrading the alternator to a 136A out of a GC. I would wire a "constant on" battery bus to take care of the radio and clock (should I do this for the ecu as well?) so if I turned both batteries off these components will not lose memory. I plan on putting the second battery in the stock air box location and running an spectre cowl intake. What wire gauge wire would be ideal for this set up? 2G? 0G? Do you see anything wrong with this approach? Down falls? Problems? Things to consider? Well thanks for all the input in advance.
atriot:'Mericaatriot:

This link may be helpful.
Also...
I don't know what you do with your jeep when you go camping, but dual Red Tops + contactor & cable + GC alternator sounds like a ton of money spent for dubious gains. I used to live / camp in my Jeep full time... never had a problem with factory electrical system.
If you want dual batteries I'm not going to tell you don't do it, just saying, examine what you really realistically need and *then* spend the money to get it (assuming you don't already have it). Maybe a single fresh high capacity battery under hood, upgraded mains & some LED interior lighting would do you?

My "dual battery system" consists of a single yellow top optima, a portable quiet generator, a Schumacker charger/jumper, a booster pack, and a spare lead acid starting battery which mainly just sits in the back of the vehicle. Its very utilitarian and has redundant backup capability built into it. Didn't cost much more than a dual system either. I agree with Yossarian's assessment.

If your second battery is mainly for self jump-starting, why not get something physically smaller? Odyssey PC925 provides the same CCA as factory in a small package. This is what I use in my dual battery setup.

The 1/2/both/off switches for batteries are sometimes called 'idiot switches' because 'some idiot leaves it in the wrong position and gets stranded'. I have been very happy with this: http://www.hellroaring.com/bic75300.php. It still allows manual isolation/combination of the backup battery, but bases automatic combining on system voltage rather than ignition. This protects you in case of alternator failure and also allows you to charge both batteries with a solar charger.

Here is the volt meter I used (wired in the way you described): http://www.adafruit.com/products/575

Thanks for the info. That is exactly what I was looking for ,an "assessment".

yossarian19:
that link was helpful and was pretty much what I had in mind but add a contactor for both batteries. I already have the red tops I pretty much got them for free (both of them, long story) I usually don't use my jeep except to get to the camp site and out, but I am worried about a dead battery, it has the AW4 so no push starting. I carry my wife and kid out camping with me and we go for four to five days at a time. The whole thing was " hey I got the batteries, why not?" Also I am going to be adding a cradle mounted winch to my packing list, and want the added security of the second battery ( I know the red top isn't ideal for winching).
jeepingben:
as far as the "idiot switches" I am not to worried about me becoming the idiot(haha), I am very anal with any gauges in any of my vehicles especially in the XJ. I am sure I glance at them at least every minute or so to make sure everything is good. As far as the pc925, I may have to look into that, Would I use it with the isolator and both batteries connected to the jeeps electrical system in a self jump scenario? or would I remove the dead battery from the system and just use the 925 to crank the engine? With the reserve of the main and the reserve of the 925 wouldn't the main just suck the charge out of the 925 and possibly leave both batteries to weak to crank? Man, I know I am asking a lot of info but I want to make sure this is going to work.

Thanks again on all the recommendations, I may get rid of one of the red tops and just upgrade the factory wiring and alternator, if that is the best way to go, we camp miles away from any main roads and the last thing I want is to try to leave and the jeep not start with my wife and little girl with me, they wouldn't be to happy lol. Thanks guys.

atriot:"Mericaatriot:

I run dual batteries with a similar setup, two full sized batteries wired through two switches. I love it, especially on longer camping trips by myself, never have to worry about leaving the radio or lights on too long and getting stranded. I think it's cheaper and more practical than an isolator.

I used 2 gauge wiring, just the stuff from home depot, it's almost impossible to bend but if you're worried about cost, it does work. The switches are 175A continuous, I think 1000A peak but don't remember exactly. The only thing I had to do was directly connect the winch to one battery, because it can pull up to 400A at full load. Built a box for the switches in front of the 4wd handle, fit nice and easy, plus there's a big rubber grommet up there on the firewall, so easy to route those big heavy wires.

lllewis87 said:

Would I use it with the isolator and both batteries connected to the jeeps electrical system in a self jump scenario? or would I remove the dead battery from the system and just use the 925 to crank the engine? With the reserve of the main and the reserve of the 925 wouldn't the main just suck the charge out of the 925 and possibly leave both batteries to weak to crank? Man, I know I am asking a lot of info but I want to make sure this is going to work.

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That was confusing to me too. The hellroaring page does a good job of explaining it. A 'dead' battery is still around 11 volts and while cranking, the voltage of a good battery might drop that low, so you combine the good battery and the dead battery for starting. I accidentally tested my system by leaving my oversized rear dome-light on for > 1 day. My main battery voltage had dropped to ~8. I pushed my aux-battery switch, waited 5 seconds, and it started right up.

This is what I used to run. I re-arranged it a bit now that my jeep is hacked up more, but I ran it setup just like this for about 5 years.

Not sure why you need a separate voltage gauge, the one on the dash works just fine, flip batteries if you want to see the other one.

I was wrong about the PC925, my backup battery is a PC1200.

Here are the other pictures of my setup: http://www.jeepingben.net/zen/zenphoto/index.php?album=2013/Jeep Dual Batteries

thanks for all the info guys. I think I am going to upgrade the altertnator and all charging wires before I do the dual battery install. What kind of tray (cost is a concern and junk yard parts would be great) can I mount in the air box location for the second battery? could a stock Cherokee battery tray be made to fit?
jeepingben: thanks for getting me the info on the batteries. So theoretically speaking the odyssey battery will start the jeep on its own right? So instead of flipping the switch and waiting five minutes I could just turn the main off, turn the aux on and start? I like your set up and may do mine similar when I figure out what battery I am going to use whether or not to run the dual red tops. My main concern about running two 1000CA reds tops is the 2nd is going to be overkill I think (but maybe a good thing if I have to use my winch?) and the red top weighs a ton.
Rednek: nice set up you got man, I want a separate voltmeter and three way switch so I can monitor either battery even when it is off the system, to check its state of charge. I want to be able to check the batteries straight off the battery when it is disconnected from the jeeps electrical system to decide if it needs to come online to charge. Also where did you buy your switches from? they look like tractor battery switches.

So as of now I am pretty sure I am going to do the dual battery set up and am unsure of how to mount the 2nd battery where the airbox was. I want inexpensive but secure and strong. The forum is awesome thanks for the help!!!!

atriot:'Mericaatriot:

If you want to get *hella* crafty, you could get a battery box and put your second battery in the back when you need it : mount an Andersen connector to the box & leave the battery in the garage when you don't need it. Let's you keep your factory air box, for one thing. You'd also then have an andersen connector in the Jeep, good for air compressor or jumper cables or second battery or...

lllewis87 said:

thanks for all the info guys. I think I am going to upgrade the altertnator and all charging wires before I do the dual battery install. What kind of tray (cost is a concern and junk yard parts would be great) can I mount in the air box location for the second battery? could a stock Cherokee battery tray be made to fit?

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I made a custom tray for the PC1200, I don't think you could go much bigger. My intake is from Rusty's.

jeepingben: thanks for getting me the info on the batteries. So theoretically speaking the odyssey battery will start the jeep on its own right?

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Yup

So instead of flipping the switch and waiting five minutes I could just turn the main off, turn the aux on and start?

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5 Seconds; that was mentioned on the Hellroaring site for VERY dead batteries, for a battery that almost cranks, just hit the button and go.

I like your set up and may do mine similar when I figure out what battery I am going to use whether or not to run the dual red tops. My main concern about running two 1000CA reds tops is the 2nd is going to be overkill I think (but maybe a good thing if I have to use my winch?) and the red top weighs a ton.

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Putting a heavy battery where my second battery is can break your jeep. When I was planning my setup, some people said that area under the hood uses sheetmetal not meant to take weight. I didn't want put a battery (even AGM) in the cab since I spent $$$ to get stuff out of the cab (detours tailbone) and my OBA hoses come out of the cubby where most people put their indoor battery so I went with a small, light one.

A second battery where the airbox is will not break your jeep, the sheetmetal is the same between the two sides. You just have to figure out something to do with the intake, like a cowl intake.

I think this is the the switch I used, can't remember where I bought it from though. Link

The diesel XJs had the battery on the drivers side. the sheetmetal didn't change.

Thanks everyone for the information, ill let you know how it turned out when I get a chance to get it done.
atriot:'Mericaatriot: