This thread contains a brief description of my dual battery setup in my 2007 V-8 4Runner. I put this thread here because after searching for info on dual battery setups, it was clear most of the info is buried deeply inside people's build threads and hard to find.

Following is a description of my installation, and if you would like a more detailed account, please go to my build thread here: Sunpilot's 4Runner Official Build Thread The battery build begins on page 13 at post #187

I am building my 4R for mostly Overland Expedition type of use, so it is important to me to have enough battery reserve for extended stays in the back country. I ditched my regular wet cell battery in favor of two AGM (absorbed glass mat) batteries. The reason is because AGM batteries are more vibration tolerant, can be mounted in different positions, are deep cycle capable, and provide more reliable power. Having two batteries is a plus for Overlanding because the main battery is used for normal vehicle use, and the second (house) battery runs the extra items, such as radios, refrigerator, camp lights, water pump, etc. The batteries are separated when the vehicle is off, thus protecting the main battery from current draw while camping, and saving it for starting duties. Using this type of setup will ensure you don't wake up stranded with two drained batteries.

I chose Odyssey batteries for my installation because my research revealed many good reviews and praises for them. I was initially going with Optima batteries, but I read a lot of negative reviews, especially since they moved manufacturing to Mexico. Odyssey is made in USA, as far as I can determine, has a good reputation, and a very nice warranty. They cost about the same as Optima, so it made sense to me to use them.

For the 4th gen 4Runners with the V-8, like I have, the space to mount a second battery is limited. The air cleaner box takes up a lot of room under the hood. I put my battery behind the air cleaner on the right fender. I used an Odyssey 34 PC1500 for the house battery, and an Odyssey 34R PC1500 for the main battery. The only difference is the 34R has the battery terminals reversed and fits the stock location better. Here are pics of the two batteriers

20180322_120821 by sunpilot1, on Flickr This is the house battery

20180325_135006 by sunpilot1, on Flickr This is the starting battery

As you can see, on the 34 PC1500 the positive terminal is well inboard of the fender, and no danger of accidentally shorting on the body. Same is true for the 34R starting battery.

I'll give you some technical info on the components here, that way, I won't have to describe them again in the build thread.

I used two 150 amp fuses, one for each battery, made by Installgear. It is imperative that you fuse each positive lead from both batteries...they are both hot, even when isolated. I've seen installations that had only one fuse and I guess the owner thought it would protect both batteries, but when the batteries are isolated from each other, they still have a charge, so two fuses are needed.

I used a 60 amp circuit breaker to protect the positive feed to the rear of my vehicle, where I have another distribution box and switches mounted. The nice thing about the circuit breaker is I can open my hood and trip the breaker when I'm not using the house battery (this would stop anything from inadvertently running the battery down when not necessary.)

I used 1/0 welding cables for my battery leads, and crimped my own lugs using a cheap crimper that works with a heavy hammer... the connections are solid and tight. A note here... if you use the Installgear fuses, you do not need to crimp lugs, they have a large set screw type of connection that you simply insert the cable and tighten the screw.
Fuse
20180307_112013 by sunpilot1, on Flickr
You can see the circuit breaker behind the battery in this photo
20180325_134959 by sunpilot1, on Flickr

Cable I used
20180326_141205_001 by sunpilot1, on Flickr

The last, and most important component is the Bluesea Automatic Charging Relay. I used model 7610. It is a dual sensing relay. The way it works is it senses battery voltage on both batteries. Most batteries have a resting voltage around 12.7 volts. The relay keeps the batteries combined, or linked when they are at full voltage. If the relay senses a draw on one battery, say the house is running your fridge, the relay will automatically unlink, or isolate the two batteries. The house battery can supply energy to your camp needs without draining the starting battery. Also, the relay will isolate the batteries when the vehicle is started. It will keep the batteries isolated for a period of time to allow the starting battery to come up to full charge, and then it will link both batteries together so the house battery can charge. As long as the vehicle is running, the alternator will keep both batteries charged. This is almost a fail safe setup that works very well.
here is a photo of the relay
20180307_130017 by sunpilot1, on Flickr
Here is a description from the Bluesea installation guide outlining how the unit is connected
20180326_140932 by sunpilot1, on Flickr
20180326_135717 by sunpilot1, on Flickr

I'd be happy to answer any questions if I can, and as I said earlier, please go to my build thread and check out the complete installation here: Sunpilot's 4Runner Official Build Thread I should have the build posted by tomorrow

did the big 3 upgarde?

I just installed a very similar setup in mine! Same ACR, similar components location and routing. I ran a 1/0 negative between the two batteries too, which after I did thought wow, why didn't I just ground them separately because I need to ground the second battery anyway for isolated operation?!?!? So I could have saved there. Also wasted $$ on the offgrid engineering battery tray in the interest of time. It is pretty stout but surely overprices. The military style battery terminals are awesome. For crimping the lugs on, I used a $20 hydraulic crimper off of amazon and it worked great, I think much easier than the hammer type would. I still need to get a new starting battery but should be plug and play with 34R. Might use my new 34R there and put a smaller house battery on the tray. I learned a lot from following Brady Adventures youtube channel and Bumbo's threads on here. Congrats on having cold beer!

I didn't replace the alternator cable, which I think is part of the Big Three

The instructions say to run a ground between the batteries, and I used 1/0 as you did. I think it's the proper way... sometimes chassis ground can get corrupt, so peace of mind and with 1/0 cable there is plenty of flow for little loss.

I couldn't see spending a ton of money on a battery tray, so I built my own. I'll have a detailed write-up of my battery tray in my build thread in a day or so.

Dude you're a life saver. I plan to do this, this coming spring to my 06 v8 4runner.

Is there any chance I could call you to ask you a few questions?

great read. Will be coming back to this as soon as it warms up a little.

I've been thinking about this as well. Is there any way to be able to run the in vehicle electronics from the aux battery? I would like to have a system that isolated the batteries upon shutdown but still allowed the radio, cabin lights, cig lighter chargers, ect to still run. The way yours work the vehicle is essentially shut off and all the aux battery is powering is an outlet in the rear correct?

Yes, its pretty easy for most items.

My entire stereo system runs off the AUX battery… It’s a matter of re-wiring the radio head units main power (or any other load for that matter) to the AUX fuse panel.

You can install a separate switch (like a 3 pole switch) to select between the factory ignition controlled on, or the 12v aux to trigger it on, but the radio main power if fed from AUX at all times.

Things like outlets, USB, cig... mine run 100% fed off the AUX panel. If the car is running, its being powered off alternator anyways as both batteries are in parallel. No need to complicate wiring.

I also highly recommend using Anderson plugs... you can hot swap accesses even more conveniently that a cig socket, and run much higher current loads. I have a few around the truck for my convenience. Fridge, inverter, chargers, tent power can all my added or removed in seconds.

Can someone point me to a schematic if it’s available that shows how to wire everything so it isolates the vehicle and accessories to either both batteries (vehicle on) or house battery (vehicle off)? Basically I want to be able to use the 12v plugs already available in the runner as well as the oem sound system while the vehicle is off. If that is a poor way to go about it let me know. I have two light bars, Cb radio, and plan to install some plugs and additional lights in the back (plan to sleep in the runner on a platform).

Unfortunately it's not as easy as we would like it to be... if you want to use your factory accessory outlets from the house battery, then you will need to re-wire them to be supplied from the house battery.

This includes the stereo. I re-wired the main power to the house battery, and put the "turn on / signal wire" on a 2 position 3 pole switch. This allowed me to choose if I wanted the stereo to be turned on by ignition, or just manually without a key in the ignition.

Once you re-wire them, then by default its power by house when the car is off, and supported by both(alternator) when the engine is on (provided are using something like that BlueSea ACR)

I also found it better to just run a new dedicated line to the accessory instead of mucking around with the factory fuse panel. Its much easier to restore back to stock if needed and preserves the factory electrical as much as possible.

That said, with all that work taking place, I just installed a new dedicated outlet using Anderson plugs. I am no longer limited to the 10-15 amps of the factory outlet. I have 30 amp drops all over the truck and it just worked out better for me.

EDIT: Add Info

In my experience, if you are not willing to tear down the 4Runner to something that looks similar to this, you probably won't be able to achieve what you want to do. It looks worse than it really is, but it wasn't that bad. Keep that 10mm socket handy.



To make my life easier, I decide to install a "sub-panel" inside the cab on the passenger side. The sub-panel is fed by the primary house battery fuse panel located under the hood. This is the distribution hub used to re-wire factory outlets and power to the house side.

Do you need to replace the starter battery with an AGM if the aux battery is AGM? I have the exact same setup, only with an Optima D34M, and the OEM Truestart battery. Do those batteries need to be the same chemistry to charge properly? Also if you do have two AGMs, is a voltage boost diode necessary for the longevity of the batteries?