Very Simple Dual Battery Idea

Has anyone put a simple dual battery system like this in their Tundra? I’m not seeing many DIY write-ups on dual battery wiring on the forum.



I need to figure out a way to power my fridge and some lighting in the next week and a half. This seems like a really simple way to do it. I’d run the 2nd battery in a battery box in the bed.

This is not my idea; it’s the first post in a huge dual battery thread at ExPo:

https://expeditionportal.com/forum/...eap-isolated-dual-battery-setup-for-50.77503/

 

https://www.tundras.com/threads/dual-battery-setups.6717/

https://www.tundras.com/threads/dual-battery-setup.27319/

https://www.genesisoffroad.com/tundra-dual-battery-kit

 

Thanks. I did search, and I’ve seen those threads. And they don’t answer my question. Hence the new thread.

 

. From the legendary Antman! If you've spent any time on T4R.org before 2019, you know Antman. My plan is to get two identical AGM group 24 batteries and wire them together using the diagram below. I'm not interested in the Genesis or SDHQ systems at this point. Having read a lot about this, it seems some are saying the Tundra doesn't charge AGM batteries as well. Others are saying it's fine and works the way it should.

This is the downside to deep-searching the forum. You get results over an extremely long time frame, and experiences/opinions shift over time. Feels like I'm reading too much and getting conflicting info. Need to have this sorted within a week for our trip out West. My only real need for this trip that starts a week from Friday is to power our bed-mounted Dometic CFX3 55IM.

 

check out @blackoutt build. He has link in it to the wiring he did. He tundra is rigged pretty well so I would trust what he says. it looks similar to yours

Edit: Found it for you

https://frugalfill.com/the-ultimate...system-with-solar-simple-cheap-and-effective/

 

Nice to see another T4R'r in here!

There's no real reason it wouldn't work, and IIRC, Antman's SPDT switch was to allow the solenoid to be overridden to force the batteries to either stay connected, be ignition controlled, or disconnected from each other.

I would recommend going with a PAC200 or PAC500 (or similar) relay instead of the 80A units due to the alternator's output (and potential charging) being >80A at some points. FWIW, I have a Blue Sea ML-ACR on mine, which is capable of ~500A IIRC, and also includes the override switch and automates the connect/disconnect based on voltage from either side.

For charging voltage, it really depends on what source you talk to about what the actual charge voltage requirements of each AGM is. People have quoted Northstar as saying "anything a modern vehicle puts out" as well as "14.2-14.7v", other brands seem to be somewhat variable or vague in their answers. I simply go off of what is printed on my Northstar's (14.4-14.8v). My '21 charged around 13.9-14.1 usually, so I popped in the GM Diode and I'm generally in the 14.1-14.6v range now. Yes you can run a DC-DC charger to be "perfect", but that isn't a need, at least personally. While the truck is parked at home it lives on a Victron 25A charger to keep both batteries topped off, but only because it'll sit there for several days at a time, and the fridge is in the truck and powered on 24/7.

I've got some more details of my "simple" install in my build thread, just replace any reference to the ML-ACR with any generic 200-500A relay and ignition triggered switch.

What part of the West are you headed to? We'll be up and down the coast and then heading back east over the next few weeks

 

And another one....LOL

I used to post on there (same username) but I was only there from about 2011-2013. Definitely a good bunch of guys (though God help you if you didn't search before posting....) and they got me through a bunch of work on my 2000 4Runner (replacing the motor blower resistor; replacing the ball joints/tie rod ends; replacing the rear towing wiring; replacing the brakes with larger 1st Gen Tundra brakes; and replacing the radiator).

 

We're going to do some dispersed camping in central and southern Colorado. We will be driving each day to different spots off the beaten path. I'm hoping that weekdays and harder-to-reach places will be less busy. I know CO is nuts in the summers...

I have the PAC500 on the way as well as (2) x 200A fuses, per Antman's schematic. If I don't install a SPDT switch, everything will still work, right? I would just have to jump my starting battery manually in the event it needs a jump, right? If I skip Antman's switch, will it operate as if the switch were set to "Auto?"

I'm a total noob when it comes to wiring. Thanks for the help!

 

Your setup plan looks good for your purposes so far. You don't need the switch from the Antman diagram if you just run the PAC500 switch from a keyswitch source in the fuse box, you should simply use an "add-a-fuse" to anything keyswitch power. Group 24 AGM will run your fridge all overnight even if it's stupid hot out and fridge is empty. I see you're running both batteries as matching AGM type so that's good too. As long as you're driving each day to top off the house battery this will work great and keep your starting battery untouched.

Thanks @dittothat for the plug!
I have wiring help/tools in my link too. You'll need a hydraulic crimper to get the lugs on the 2ga wire properly, do not solder, and the 3:1 marine adhesive style heat shrink is a must.
https://frugalfill.com/the-ultimate...system-with-solar-simple-cheap-and-effective/

Only other advice is to put your fuses as close to the batteries as possible.

And then as @Mallcrl mentioned get the GM diode alt-s fuse to boost alternator charging voltage slightly to be a better fit for AGM charging profile. Part number is somewhere in the Chi-town 4x4 link in my article.


Edit: oh and be sure to fuse the power to your fridge as close to the battery as possible too!
Enjoy your trip!

 

Awesome. We will be driving each day for sure. What is a "key switch source"? Do you just mean running the PAC500 isolator to an ignition-on fuse instead of one that is hot all the time?

It's looking like I'm going to ditch Antman's switch for simplicity's sake and see how we do on this first trip.

I'll definitely be referring to your page. Ordering those tools and the GM diode as well. Now to find some decent local 24F batteries! Thanks!

 

key switch source = ignition-on fuse, yep you got it!

I found that AGM 24F from autozone/advance/oreilly/napa/walmart/sams were all the same battery with a variation of 2 different styles of case, gray case black top. Their online picture almost never matched the style of case in store. I suspect they are all made in the same place with same/similar characteristics. I think I spent around $200 locally for one. I went with autozone for the purpose of easy replacement anywhere across the country with 1 day order from another store if needed, walmart was always out of stock.