There are a million different ways to install a dual battery system. However I was unable to find any details online that talked about wiring an entire system in one article or diagram. I am not an expert in automotive electronics and I am sure there are other ways to do this, however I found this solution works flawlessly for me.
The first section of this article will show my system and my diagrams. The second section will have my parts list and why I chose those parts. The third section will include what I would do differently now.
With a drawer system my options were limited. However, specifically in a 5th Gen 4Runner the location I chose would work for many as it's mostly dead space due to trunk configuration. The battery fits perfectly in the location BUT blocks the stock AC and DC plugs. I never used those plugs and find the AC plug works poorly anyways so it wasn't an issue.
I had to trim two pieces to get it to fit. The section near the tie down and the passenger tail light cover. The cover is not a necessity to trim, however you will not be able to easily open the cover without removing the battery otherwise.
The battery is secured using the two straps seen above. I installed tabs into the plastic trim and my drawer system. If you do not have a drawer system, you would simply install the second set of tabs on the cargo floor directly to the left of the battery. I also used double sided tape in strategic locations to prevent sliding around if the straps became loose.
I wanted the RedArc system to be easily visible. This would allow easy access to visually inspect the status of the system. I used a dremel and a chisel to cut off the plastic strap tabs on the battery and allow a flat install (not the cleanest work I've done!).
I then used double sided (15 pound) velcro tape to install the RedArc system onto the battery.
Any inverter I chose that was a pure sine wave system was unexpectedly heavy. Therefore I wanted it to be mounted in a secure location that is easily accessible. I had to do a bit of cutting with the dremel to get it to fit like a glove.
Power Socket Install
I installed two 12V sockets and two double 3.0 USB sockets into the tail light cover. I chose this location as it is an easy way to hide the wiring and provides easy access to the wiring if needed.
I wanted easy access to fuses and monitoring systems. I used a molle panel for the 5th Gen 4Runners and mounted a black cutting board onto the panel. The allowed me good mounting points and a clean install.
What the backside looks like.
What it looks like when all the wiring is complete (scroll down for diagram)
With paper towels
Full cargo view
Side view showing that the system takes no used storage space
Below is a picture of how I mounted my Victron Energy AC battery charger. I used double sided velcro tape.
Below is the "nipple" I mentioned earlier. It's an optional add-on for the RedArc battery system. I wasn't sure if I needed it but am extremely happy I installed it. It allows me to see if the system is working from the driver's seat. Haven't had an issue at night with it but put a toggle switch for it just in case.
Below is plastic mold I used to cover all the positive terminal connections. This was done for safety reasons. I used a product called InstaMorph. It works excellent for this purpose and is difficult to take off (the objective).
Solid red line: 6 Gauge AWG wire
Dotted red line: 12 Gauge AWG wire
Solid Blue line: 6 Gauge AWG wire
Dotted Blue line: 12 Gauge AWG wire
Green line: RJ12 Data Cable
Fuse between REDARC and 2nd battery: 60 amp (per REDARC)
Fuse between fuse block and 2nd battery: 100 amp (per fuse block manufacturer)
Fuse between inverter and 2nd battery: 60 amp (per inverter manufacturer)
Additional Diagram Notes
I used larger gauge than recommended to future proof system. I used recommend fuses.
For main ground I used the rear seatbelt bolt. You can use any bolt mounted directly to the body of the vehicle. Please sand the location to create a good contact.
The third toggle switch is not wired. It was added in case I wanted to use it in the future.
Please refer to the first photo in "complete photos" section. You will observe that some wires are not visible as they are wired at the rear of the panel.
This parts list is based on wiring the entire system in the rear of a 4Runner. The parts list would be the same for any vehicle but the lengths of wire may differ.
Battle Born LiFePO4 - 100 Ah 12V
I chose Battle Born because of reputation and dimensions. It was a perfect fit for my desired location.
I chose a LiFePO4 battery because of longevity life vs a deep cycle battery.
It is important to know where you will mount your battery prior to choosing a battery. A deep cycle can sit under the hood. A Lithium battery cannot sit under the hood due to heat. A lithium battery needs to operate at or below 170 degrees F. If it is inside your cargo area; it should be fine. If it is in the shell of a pickup; I would strongly recommend creating some kind of ventilation.
RedArc Dual Input 40A BCDC1240 Charger
This is the heart and veins of your system. From previous experience it’s easy to not pay attention to your charger as you always assume it’s working. And then you have a problem when you system fails day 1 of a 5 day trip. The charger has a lot of electrical chips/boards. From my experience boards tend to go bad when wheeling hard off-road over time. Therefore, I went with the most trusted system for off-road use after watching their quality testing videos.
I chose a 40A over a 25A to future proof my system if I want to add extra batteries.
Victron Energy Blue Smart IP65 12-Volt 10-amp Battery Charger
This is to keep your system charged at home if you leave it parked for a few weeks. I chose Victron because they are a top-of-the-line manufacturer.
I did not choose Victron for my main charger because I did not locate any information on specific off-road/heavy abuse testing.
AIMS Power 600 Watt Pure SINE Inverter 12V DC
I would recommend Victron Energy pure sine wave inverter (whatever size you need). I found their inverters to be too large to fit in my desired location and therefore I went for the lessor brand.
Victron Energy BMV-712 Smart Battery Monitor
This isn’t necessary but gives me piece of mind. Victron has the most options (including Bluetooth) to monitor the state of your battery. I want to park at camp and see exactly how much juice I am pulling and how long my battery will last.
(1) Nilight 6-way blade fuse block - 6 circuit
I chose this Amazon brand because it was available faster than Blue Sea Systems. See last section of this article as to why I would choose Blue Sea Systems instead.
(1) Blue Sea Systems 60 amp circuit breaker
(2) REDARC 60 amp fuse kits
I chose this as I expected it to be top-of-the-line quality and use. See last section of this article as to why I would choose Blue Sea Systems instead.
6 Gauge AWG cable wire (40 feet red, 20 feet black).
12 Gauge AWG cable wire (40 feet red, 40 feet black).
Heat shrink tubing – various sizes. Must be with adhesive!
(12) 6 AWG heavy duty wire lugs, battery cable ends, bare copper eyelets.
Heat Shrink wire connections (various size kit)
T-Tap wire connector kit (various size kit)
3M cable zip tie mounts with 8” zip ties
3 feet RJ12 Data Cable (black)
If using a Victron battery monitor.
(1) ARB Fridge wiring kit (only if you are using ARB fridge). Otherwise substitute for 12V cigarette socket.
(2) Cigarette Lighter sockets
(2) USB 3.0 sockets
(4) on/off toggle switches
Black 24” x 18” cutting board.
To mount wiring onto system for cosmetics and ease of tracing wires.
InstaMorph – Moldable Plastic
Battery terminal safety and Fuse safety
12V Interior LED Bar
12V light bolt – flush mount
To monitor RedArc charger
What I Would Do Different
Please note that I am very satisfied with my setup and do not plan on changing anything. After utilizing my setup, I believe I could have done a slightly cleaner and more cost effective job in relation to wiring. The points below will explain what I would consider doing different on a future project.
I would use Blue Sea Systems fuses (60/100 amp) instead of REDARC. Personally I do not see a quality difference that justifies the price of a REDARC fuse.
I would use Blue Sea Systems fuse block instead of the Amazon described above solely because Blue Sea Systems is rated up to 30 amps per fuse VS 25 amps per fuse on the block I purchased.
I would consider using a positive busbar so I would only have one wire going directly to the 2nd battery and not four as I have now.
I would consider using a negative busbar so I would only have one wire going to the shunt and not three a I have now.