Has anyone here installed a second battery on the passenger side behind the air filter box? If so, what size will fit and what parts are needed to actually install this? Going into a 2016 TRD Pro with a TRD CAI.

C4 Fab makes a nice box to mount a second battery in that location. You'd have to check their website to see what fits but something like a Group 34 fits in that spot as I had one there on my 4th gen.

As far as what else you need, I'd look at a Blue Sea ML-ACR for switching and then if you use an AGM, you'll need a DC-DC charge booster. Cabling etc. There's tons of shit written up about this as it's been a popular mod for decades.

I did this kit, using this video as a guide. It took me 2 days due to frequent pauses for back pain. Easy install:

'10-Current Toyota 4Runner SDHQ Built Complete Dual Battery Kit

An idiot?s guide to a dual battery setup on 4Runner - YouTube

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Here is a link to my install:

https://www.toyota-4runner.org/3172443-post77.html

Here's a pretty damn fine thread on dual battery options

Dual Battery Systems

Follow the above links for info....

FWIW, I have the C4 Fab battery tray and am using a Northstar 27F AGM... I don't think anything even slightly longer than the 27F would fit; I'm using a Battery Doctor 150A battery isolator to isolate/combine the two batteries and a ArcLight voltage booster. I ran 1AWG between each battery and the isolator. and am using Blue Sea MRBF fuses at each battery. Current flows from the second battery to 2 separate Blue Sea ST Blade distribution blocks under the hood (a 6 outlet and 12 outlet, one on each side), a 6 outlet ST Blade block under the dash (through a relay to create switched power), and to a 12 outlet ST Blade block in the cargo area for power to all the relays in the back and all the outlets/rear powered accessories.

Since I have a fridge that lives in the truck and the truck regularly sits for a few days at a time in my driveway I'm also running a Victron 15A AC-DC charger and plug the truck in anytime I'm at home and have the ability to plug in a portable 120W solar blanket in the event we are at a campsite for more than a day or two (campground style)

Thanks for the info so far everyone. Just as an FYI, I am running a X2Power/Northstar 31M now as my primary with the ArcLight voltage booster. I may be able to get a second AGM battery for free, so I was considering dropping it into the passenger side and set it up for the moment until I can decide what else I want to run off it, I have been considering getting a frig.

Most people use them for refrigerators and other accessories/appliances they have in the rear of the vehicle. The intro on the video in the third post explains it.

correct, it's needed for my fridge when camping. in addition to that, i can use it as a jump pack just in case my primary battery dies when i'm somewhere with no help.

I wish I understood what was in these threads, I am plannin on getting a fridge but still can't figure out how to do a second battery.

The video in the 3rd post does a great job laying it out.


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Seriously? Dude you've already created two separate threads on dual battery systems with plenty of replies and good advice and you still don't get it? Not to be an ass but if you don't get it by now then just take it to a professional to have it done. It's that simple.

Threads you've created...
Is there a easy way to install a dual battery
Will I need a dual battery?

Oh I know, I just don't want a fire, people say if you do it wrong it will start a fire. Also most of the links to parts are dead and not to what they say they are.

I was thinking about a second battery/solar set up with one of these batteries...
50AH LifePo4 Battery

I've been slowly building a small 200w portable DIY solar system for camping and power outages at my house, but now I'm thinking about building it in the 4Runner instead. I'm basically needing to charge my Ryobi 18v batteries which I use for all kinds of things camping (fans, lights, saws, small inverter) and for emergencies and power outages at home, plus charge AA batteries/phones/ipad, and maybe some LED lights. They can all charge by DC only so it can be a very basic 12v system. At most I may power a 12v cooler fridge down the road, but no need for it yet. Anyone done something similar?

Maybe I'm just old (or old-school), but does no one else remember that a bunch of house fires were caused by mixing aluminum and other metals in electrical circuits in the 70s? It can be done, but randomly connecting bare aluminum (in the battery terminals in that kit) with other metals, especially bare copper, is a hard pass for me.