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Old 09-13-2007, 12:22 AM   #1
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HOWTO: Dual Battery Setup

Back in August of '06 I installed a dual battery config in my TJ. Well I finally remembered to post some pictures:

Here's a pic of the "tray":

And of the top cross bar:

And the final product (before reconnecting everything):

Here's a pic of the wiring diagram I drew up:

Shopping list:
- Optima Red Top for main battery
- Optima Yellow Top for all accessories
- Painless Wiring Isolator
- Mean Green 200Amp Alternator
- ~20' of red and 20' of black #2 stranded cable
- a couple feet of 1.5" x 1/8" angle
- a few feet of 1.5" x 1/8" flat
- other: heat shrink, lugs, and wire ties

I set it up with the mindset that everything that came stock with my TJ went to the main battery and everything I've added (lights, winch, CB, etc) go on the accessory battery.

Chose the painless wiring isolator because there is a connection into the cab (not shown on the pic) with a switch that can allow for 1) normal operation where both batteries are being charged, 2) splitting off the Aux battery so it is completely by itself (i.e. not being charged), and 3) connecting the two batteries together in case the main is dead and you need to basically do jump it (with no jumper cables) to start the vehicle.

Uses the stock J bolts to hold it down. The two ends of the cross bar that aren't touching the J bolts are bent at a 90 degree to stop the batteries from shifting side to side.

And I used about 1/2 a can of spray on bed liner to coat the metal cross bar (figured it might make a nice rubberish coating on the cross bar).

In all was a fun project...especially since it was my first.

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Old 09-13-2007, 01:06 AM   #2
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Why would you want this?


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Old 09-13-2007, 01:16 AM   #3
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Originally Posted by ripbiker13 View Post
Why would you want this?
Winch/Lights other stuff that would run off a bat, and that you dont want to drain your main.


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Old 09-13-2007, 02:59 AM   #4
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yeah i need another battery my lights dim just with my stereo loud and when my winch is working.....I want to add 4 130w lights to the front of my jeep and 2 on the back and also rock lights
06 Rubi Unlimited, 3.5" Rubicon Express LA, OME Shocks, Metal Cloak Aluminum Bumper, Warn Winch, Power locks/remote start.
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Old 04-12-2010, 01:25 PM   #5
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Master Switch?

Nice setup! What do you think is the feasibility of using a heavy duty power-switch as an axillary battery master switch instead of an isolator?
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Old 10-16-2011, 11:09 PM   #6
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I like the set up, thanks I was looking at the other side tray, probably for when the steering wheel is on the other side? I think I m going to put my tank and compressor on that side. Do you have air too? Thanks for pics
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Old 11-21-2011, 08:25 PM   #7
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Nice Set-up btw, the other tray is not for if the steering wheel is on the other side (my TJ is a Righty) it is actually for the ABS module.
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Old 11-21-2011, 09:53 PM   #8
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Thats sweet... I need to do that and was thinking of using the other tray instead of squeezing it in. But now I know they will fit. Thank you!!
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Old 09-08-2012, 04:00 AM   #9
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Is optima a good battery? Mines great and has never let me down. I was just wondering.
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Old 09-08-2012, 06:09 AM   #10
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My red top has survived a jeep fire, wrecked truck, & now it lives in our Massey 235 with no alternator
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oh and when i find the guy who invented torx screws i have a big can of wup-ass for him
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Old 05-09-2013, 08:27 PM   #11
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Any pictures of the control you use to switch between the batteries?
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Old 05-09-2013, 08:32 PM   #12
Knows a couple things...

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Originally Posted by Texas2070 View Post
Is optima a good battery? Mines great and has never let me down. I was just wondering.
Optimas used to have a superb reputation but not since Johnson Controls bought them & moved all of their manufacturing down into Mexico. I had two Yellow Tops & one Blue Top all fail prematurely, I wouldn't run an Optima any more if it were given to me.

Nice job on the review Reketr. I noticed the mix of Red Top & Yellow Top, just remember to never let them get connected in parallel with each other. The only way batteries can be connected in parallel without one damaging the other is if both batteries are identical in every way including age.
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Old 05-09-2013, 08:45 PM   #13

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Originally Posted by Jerry Bransford View Post
The only way batteries can be connected in parallel without one damaging the other is if both batteries are identical in every way including age.
This is simply not true, we connect truck batteries (the average class 8 truck takes 4 very large high CCA batteries) 1,2 and 3 or 4 at a time all the time, no ill effects. Some large equipment that takes 8 or 10 or more rarely get all changed at once, you use a temp gun or voltmeter to find the weak batteries in a set.
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Old 05-09-2013, 10:05 PM   #14
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The wiring diagram indicates that connecting them in parallel is exactly what he is doing...
Always Remember: Safety Third!
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Old 06-29-2014, 10:06 PM   #15
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Duals in my 06 Rubicon

A hearty hat-tip to RKETR for this thread--I've been running one of the stacked dual battery setups in my Rubicon and disliked it for several reasons:

--The lower battery is impossible to see;
--relocating the electrical box to make room for the upper battery precluded installing an Airaid intake;
--In my view, they are fire hazards with side terminal Optimas--despite using additional shielding, I had one battery almost short out to the tray due weight/compression/vibration tearing insulation almost down to the terminals
--very hard to access terminals if you need to use jumpers

So when I saw this thread, I took the hint but a slightly different route--I can marginally tack fairly thick metal together but wasn't about to try to tack weld to sheet metal in the firewall. I'd have a hole, and likely a fire. So I fabbed a cradle for the batteries, following the general layout here.

First I had to nip off a couple protruding screws--Dremel time.

Next, using 1/8" thick angle iron for the side bars, I tacked 1/8" flat stock to serve as a cross bar. After several dry runs where I riveted a dummy setup together, I bolted the crossbars in place (3 using the original holes; I drilled the after/driver side hole so to give a better, more supportive angle to the crossbar; used the same retaining nut as stock) and with the one angle iron in place, tack welded it.

Then I pulled that out, and built the rest of the cradle on the bench, riveting it first, trying it, then welding it. I could have used just two cross bars, but added a couple and put some heavy, closed cell foam on the cross bars to provide a modicum of support, damping, and tackiness to keep the batteries from shifting.

The top piece was the bugger--this is the first version; I wound up whittling it down quite a bit to get clearance on the wretched connection block that mounts to the firewall. I could have remounted that a bit higher but that was more work than I felt like at this point.

I also discovered, to my chagrin, when all was bolted in place, the driver side battery was just touching the A/C can. So I did some strategic whittling, and gained 1/4 inch. BTW, the none-side terminal battery is a tad smaller than the side terminal; would have been a tad easier to do this if I had two non-side terminal batts instead of just one. Anyway, here's the installed setup, with a messy, temporary job on the cabling. I need to re-run that anyway was the Airaid intake I added at the same time had a little impact, and I'm getting some heavy duty terminals anyway for all the connections.

Lastly, to preempt some of the observations I've seen in this or other threads:

Are dual batteries needed? Ans: Depends. I want them because I hike and hunt a lot in remote places, alone, and a dead battery in bad weather in a deep canyon on a hot day is not a problem I want to solve. Right now my setup is two batteries, isolated, with winch and accessory lights run off one, starter/stock vehicle needs off other. Warn isolator has worked fine. If you're not prone to put yourself at risk as I do, then a heavy duty alternator and gel cell battery will likely do you just fine in my opinion.

Airaid--not the topic here, but the mere mention of CAI seems to provoke debate so here's my two cents: I've seen enough credible research to show it does give decent hp/torque boost, albeit at mid/high ranges. But that helps me, as there are two nasty pulls going north out of Phoenix and one coming back. As I haul water up and firewood back to my little place in paradise, it's nice to have a bit more power. And it makes a difference in town--as if I pulled maybe 200 pounds off the rig. Not startling, but nice. If I lived in a flat place, or didn't drive at high altitude, I wouldn't have messed with it.

So there you have it. This solves all my gripes with the stacked setup, cost a heck of a lot less, and turned out to be mega-fun as I used a self-darkening welding helmet for the first time and it improved my welding by about 300%. Not that it makes it fit for public viewing, but I had fun....
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Old 06-29-2014, 10:08 PM   #16
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So the warn isolator is what lets them stay charged yet separate?
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Old 06-30-2014, 12:10 AM   #17
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Originally Posted by Majnoon View Post
So the warn isolator is what lets them stay charged yet separate?
Exactly. It directs the charging to the battery that needs it while keeping the two separate electrically
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Old 06-30-2014, 12:12 AM   #18
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Originally Posted by mccgsm View Post
Exactly. It directs the charging to the battery that needs it while keeping the two separate electrically
Cool stuff. Thanks man.

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