My Version of a Dual Battery Setup
 

Alright so everyone who has a Jeep has fantasized about a dual battery setup. Most people with XJ's will reroute the air filter box to a cowl induction intake. That has plenty of benefits, however I do not have overheating issues, and actually prefer the look of the stock air box. This is how I am going to run my dual battery setup! Stay tuned!

Battery Placement
 

Because I am not going to reroute the intake, I am left with limited options. First and foremost, I absolutely do not want the spare battery installed in the cargo area or under the rear seats, so I am left with even more limited options. This is what I've decided to do.

I have a 1996 XJ, which has the windshield washer resivour located on the passenger side. I believe in 1995 they started stamping the driver side inner fender to accept the 97+ relocation, so it was a pretty straightforward install. That can be found here:

https://www.cherokeeforum.com/f2/win...ervoir-262090/

https://cimg8.ibsrv.net/gimg/www.che...051e4f8916.jpg
-96 with a 96+ windshield washer reservoir

After I did that, I had a void in the engine bay that us begging to be filled with an aftermarket treatment.

https://cimg8.ibsrv.net/gimg/www.che...f7074ab959.jpg

This is where the new battery will go. It is an absolutely tight space! With the space restraints, I will have some very unique challenges. The void is nearly exactly the length and width of the battery not the height. This will be a problem to overcome. It actually may not work out! I guess I'll be the one who tests it out for everyone else 🤣

Big 7 Wire Upgrade
 

To prepare for the new battery, I've installed the "Big 7" that every Jeeper knows about. I went with 2 AWG, which is absolutely overkill and completely unessarry, but I was already going to do it so go big or go home! That forum can be read here:

https://www.cherokeeforum.com/f67/bi...pgrade-263474/

https://cimg2.ibsrv.net/gimg/www.che...0e861873ef.jpg

Auxiliary PDC Plans
 

Now that I have the space allocated and the stock wiring up to par, now if officially time to focus on how I am going to tackle my version of a dual battery setup. As I talked about in my Big 7 forum, I want to add an additional PDC for the secondary battery. The reasons for this is because I do not want to molest the original harness in case if something were to go wrong, it is easier to diagnose where the problem falls starring with which system it involved, primarily or secondary.

After a lot of research and thinking, I finally found a PDC this will work with my needs. I wanted an OEM PDC for a stock look but also so it's easier to draw up a schematic because there's already one for the PDC in that year's FSM. I wanted one with a lot of large relays. The older ones had an entire row down the side but I did not like how the cover opened and the newer the year that I pulled from the better condition it would be in. My 1996 shares electronics with both generations and I wanted one similar because even though I'm doing a functional upgrade, asthmatics are very important to me. Some only have 2 large relay slots but I found one from a 97+ with 4 slots.

https://cimg4.ibsrv.net/gimg/www.che...3ca692b9d0.jpg

This is going to be a lot to do in order to get it to work properly, but if we take baby steps it will go much easier. First thing's first, I need to prepare the new PDC and harness.

Auxiliary PDC Preparation (Part 1)
 

Alright so this thing was crusty when I bought it from my local junkyard. First thing to do in order to repurpose it for my uses is to clean it, and field strip it. Let's get started.

https://cimg7.ibsrv.net/gimg/www.che...a5751204ed.jpg
I did not need many of the connections so when i removed it i just snipped them.

https://cimg5.ibsrv.net/gimg/www.che...204c5588e1.jpg
I removed all of the electrical tape, friction tape, and corrogated tubing. I started at the PDC and worked my way the very end cutting the connectors and aligning the wires. I tried to salvage as much of the wires going up to the PDC but many of the wires were connected in between electrical connectors not the actual PDC.

Now that I have everything organized, I have a small problem; I will not need most of the wires until I have I have an electrical accessory for that fuse or relay. I have a few options. The most logical one I think would be to de-pin everything I'm not going to immediately install. The problem I have with this is I don't want to remove everything in order just to add an insignificant or small modification. So I could just leave everything attached and bundle it all up in the engine bay but that's not optimal either. Another concern I have is I don't want to handle this any more that what I have to because I do not want any pins to become loose. So I think what I going to do is install a 40 pin connector right after the PDC so I can seperate the harness from the fuse block. Honestly, this is how they should come from the factory, but what do I know. This is something i am thinking:

https://cimg4.ibsrv.net/gimg/www.che...6083c16b8.jpeg

It has pins for the larger relay wires and smaller ones for the fuses. Let me know what y'all think!

Auxiliary PDC Location
 

I have a few options where I can mount it but I think I've got my mind made up.

https://cimg5.ibsrv.net/gimg/www.che...ef3051f57f.jpg
I can mount it in the driver side corner with some wire management but it wont be close to the second battery. I think I have a better idea

https://cimg1.ibsrv.net/gimg/www.che...ba11db2337.jpg
I think this would be optimal. All of the electronics would be on the same side so it would be easier to wire, service, and better aesthetics.

There's a few downfalls with this location along with space restraints that I will have to address:
1. Reroute the cruise control vacuum. The reason for this is because in between the factory PDC and the fender I plan on horizontally mounting the circuit breakers that protect the PDC's. Right now I have the starter battery's circuit breaker mounted vertically on the fender from when I did the big 7 upgrade and I seriously do not like it.
2. Modify the bracket. The bracket with be easy to modify because I have the one from the new PDC and they are simply riveted together. I'll just remove the new PDC bracket and add it where the coolant bottle currently sits. Both PDC's will have to sit forward closer to the starting battery to allow space for the new battery.
3. Reroute the coolant overflow resivour. This one is simple and a little complicated at the same time. The bottle is too tall to go anywhere else, so I'll have to use a different container. This is kind of upsetting because I want to keep this looking as stock as possible and I would absolutely love to keep the yellow resivour cap. The solution I have for this is using an early XJ or MJ windshield washer resivour and just modifying it.

https://cimg3.ibsrv.net/gimg/www.che...9b88182666.jpg
I will have to modify it to accept the yellow cap that I love so much. I will also have to delete the pumps and add the inlet hose connector, and overflow hose. This could prove challenging because I am a perfectionist, but that sounds like a problem for my future self.

The other option I have is this resivour I found but I am unable to find more information on it:
https://cimg1.ibsrv.net/gimg/www.che...bea7bf0a57.jpg

https://cimg2.ibsrv.net/gimg/www.che...14ace0754.jpeg

https://cimg3.ibsrv.net/gimg/www.che...b47bb947b6.jpg

If anyone could point me in the right direction or provide me with information on what models and years this was released on, it would be much appreciated.

As always, thanks for following me! Feel free to like subscribe and comment! I love to hear back from the community!

It looks to be from a 87-90 2.5L

https://www.quadratec.com/products/51216_02.htm

What size battery are you able to fit? Looking to add a second battery this spring...

That's what I was thinking but I juat couldn't find a replacement part or a listing. And I may have to go with a non-conventional battery, like smaller vehicle

Do understand that with two different sized batteries, you'll need to use a DC-DC charger to keep the smaller battery from being hammered on. Could likely downsize the main battery to keep them the same and use a solenoid/isolator instead, resulting in more total capacity than just the original. A 25A DC-DC charger is sufficient for most overlanding-type uses I hear; a 60A model may work well enough for light winching work. I haven't fully thought through what it would take to switch between DC-DC charger and direct parallel without simply rewiring it. In this part of the country, its extremely rare that I would ever need to winch for a long distance, so perhaps just rewiring it when I need to is the way to go.

Here's another install I found. I change my oil filter from the top, so I'm not sure how well I'd like this version, but interesting none the less...

https://www.ausjeepoffroad.com/forum...ad.php?t=46577

Plan B
 

So I've done some research and this is what I've found out. The skinny coolant reservoir is from Jeep MJ and XJ that are equipped with the 2.5L. The slight downside is there's a feed/return line for the coolant, but not an overflow port like the 4.0 resivours have. This wouldn't be a problem at all because I can find these on Quadratec for $20 brand new (and it will accept my stock cap which is important to me) but unfortunately for my build, I've done a 97+ windshield washer reservoir swap and the fill point for that is right in the way where this needs to go. So it looks like I will have to figure something else out.

Correct me if I'm wrong but from what I've read online, different size batteries are fine if the battery type is the same. As long as proper electronics are kept (using an isolator, fuses/relays, proper gauge wires, etc.) then a smaller battery will be fine because both batteries are the same type, just different capacities. Keep in mind, the only thing I'll be using this spare battery for is accessories such as a winch and lights so it will stay fully charged most of the time.

I fit a Group 65 battery in the stock location and along with a 120 amp alternator it powers everything I have easily.

I tend to go a bit overboard on things... You'll need an isolator and the same type of battery, but as you said, for normal stuff with the engine running, it'll work just fine.

Thanks!
 

Everything I do is overboard 🤣 I tend to over-engineer and bulletproof things mainly because I want things to be proper but also because I do not want to work on it again. Anyways, thanks for your input!

I also thought about just running a single battery since I've already did the 160A alternator upgrade but I want to be able to run the battery dry (if need be) and still be able to start the vehicle