Dual Battery Setups

Discussion in 'Electronics' started by tx_shooter, Jun 22, 2017.

  1. tx_shooter

    tx_shooter Looking for my missing spare time Staff Member

    We had a decent conversation about different dual battery setups going a few weeks ago mixed into the BS thread I think but it was hard to follow just the dual battery info. So let's see those dual battery setups and parts info if you have it. I think I will be running a dual battery setup pretty soon and I want to do it right the first time.

    I would like to setup my rig where the accessories will run off the house and start battery until the switch senses the start battery is too low. Then the switch needs to turn disconnect the start battery and run the accessories on only the house battery. Anyone have a setup like this already?

    I am currently leaning towards getting this isolator without the wiring kit to setup my dual batteries.

    Amazon.com: 140 Amp Dual Battery Isolator by KeyLine Chargers (Iso-Pro140 Pro Dual Battery Kit): Automotive
    Last edited: Jun 22, 2017
  2. tx_shooter

    tx_shooter Looking for my missing spare time Staff Member

    Ran a test today with my Dometic fridge half loaded with water and beer in the back of my 4Runner. I checked the voltage and cabin temperature hourly (mostly) so as to record the voltage drop on the battery. The windows were cracked just a little bit like I normally leave my windows cracked. The test battery was my 25 series AGM out of my 87' 4Runner. I am letting it run over night to see how much voltage the battery loses over night.


    Purpose of all this is to get a real measurement for how fast the fridge will drain the battery so as to setup the dual battery system with a battery that will meet my needs but not be excessive weight/ size.
    TacoXpo and tex like this.
  3. TacoXpo

    TacoXpo TLA

    What temp do you think the fridge is inside?
  4. tx_shooter

    tx_shooter Looking for my missing spare time Staff Member

    I confirmed it is 33-37 degrees F every reading by opening it and checking the freezer thermometer inside it. I had it set to 35 degrees.

    Update - I checked the setup around 7:30 this morning and the fridge was turned off. The battery was showing 12.12 volts on the multimeter. It was still 37 degrees inside the fridge so it held pretty well over night. The battery did run for 10 hours at least but it failed sometime between 10:30pm and 7:30am.
    Last edited: Jul 2, 2017
  5. CowboyTaco

    CowboyTaco Well-Known Member

    Glad I searched for a dual battery setup thread before starting a new one. @tex and I have been discussing dual battery setups and figure this might be a good place to record the output of our research.

    We are still currently building setups, but I think Aaron has most of the parts necessary.

    Rig: 2014 4Runner TEP
    Fridge: ARB 37L (I Think....may be 35L...whatever size is closest to that is what I have)
    Other electrical accessories: 30" Opt7 Lightbar

    Battery Tray: C4 Fab.

    Battery: To be purchased.

    Leaning toward the Duralast Group 35 AGM to go in as the starter and use the OEM starting battery as the house battery. OEM starter battery is an 80D26L....which according to BatteriesPlus is just a Group35. Given that we are halfway through 2018 and we bought the 4Runner new in January 2014, it's at least 4.5 years old. We have a newborn in the house and I'm not about to leave a 4.5 year old battery as the starter and risk leaving my wife and two kids stranded somewhere during a Texas summer. Once the OEM starter goes, I'll look to put in something else.

    According to Choosing a Battery for your Overland Rig, The Duralast battery is made by Eastern Penn, which is preferable to Johnson Controls. He also states that for running a fridge, a deep cycle battery is not necessary. While deep cycle was a strong inclination at first, the warranty on them is significantly shorter than that of a regular battery. I like the idea of being able to completely drain and recharge regularly, but I also like the idea of just going to get a new one when it takes a crap. I'll probably go with the Duralast Group 34M AGM battery as the House battery when the OEM one finally craps out. Reason for the 34 is it is a little shorter than the 35 and should fit in the tray just a little better. A Group 27 should also fit if it has a flat top with nothing but the posts sticking up, but that is specific to this rig/battery tray setup.

    It is worth noting that Reserve Capacity is more important than CCA when selecting a house battery.

    So, we've got the essentials:
    • The rig
    • the battery tray
    • the battery
    • the accessories to justify the fridge.
    Now lets talk about the other things needed.


    I'm looking to get one that has a built in VSR (Voltage Sensitive Relay).

    Per Dual Battery Systems | Alternator charging, how it should be done, The Enerdrive VSR has one more huge advantage in that it is Dual Sensing (bi directional), what this means is that if you have a battery charger, or solar power connected to your auxiliary battery, and that battery gets charged enough to hit the Enerdrive VSR's set points, then it will allow your charging source to back charge the cranking battery as well, making sure that it's kept fully charged too, but again, if the voltage drops below 12.8 volts, the Enerdrive VSR will again disconnect (isolate) the batteries, so how cool is that

    140A Voltage Sensitive Relay - Enerdrive Pty Ltd

    The WirthCo Battery Doctor is recommended by Van Living | How to Set Up a Dual Battery System and allows you to easily jump start without the use of cables.


    Battery Fuses

    I'm torn here. I'm between getting two 100A ANL/MEGA fuses and getting two 100A breakers. Cost seems to be about $22 regardless of which direction I go. I believe I need two of them, one for each battery. I have no preference to brand, these links are just ones that came up first on Amazon. I may try to see if I can source some locally for less.

    ANL housing and fuses:


    Accessory Fuses

    While I really like the BlueSea stuff, I don't like spending twice as much for a similar product. I think I'm going to try the OLS 10 fuse block

    Connection for Fridge
    Aaron is using the Cllena Triple function piece found here: https://www.amazon.com/Cllena-Funct...rds=cllena+12v+dual+usb+and+cigarette+lighter
    While I like the idea of the blue readout, this Ginsco gets more stars and has more reviews: https://www.amazon.com/gp/product/B01GC496T8/ref=ox_sc_act_title_2?smid=A2JU42WM4PJ26Q&psc=1

    I also like that the Ginsco comes with switches, so I can kill power at the back if I feel the need. Plus $5 is $5.

    Pretty sure I'm going to run either 4 or 6 gauge wire between the two batteries.

    Am I missing anything? What has everyone learned about various options? Is there something that I should be doing differently? Eventually, I may want to add the option to charge via solar, but I'm not there yet. Anything I need to consider to add that in later?

    Other useful links:
    How to make a cheap isolated dual-battery setup for $50 <-- really liked this guys write up. Have not yet read the entire thread.
    Last edited: May 16, 2018
  6. tex

    tex Keeper of the 10mm sockets

    Despite the deep cycle warranty being less I will probably still go that route. The Super Start group 34 from O'Reilly is the front runner. I would have my fridge, rear usb plugs, and 30" light bar hooked up to it.
    After I get the dual battery set up going I plan to start researching a solar panel. In my head I picture being able to mount a 100w panel to my rack and fit between the rails so it's flush.
  7. Silverback

    Silverback I'm not always a dick. Just kidding, go fuck off

    I would skip that fuse block. Those little blades will fatigue and fail over time. As for the Blue Seas being 2x the cost, maybe true but its still only $25. Money well spent.

    As for connecting the fridge I would skip a 12v outlet and just hardwire it to the fuse block. You can buy an extra harness and just cut the cigarette lighter plug off it.

    Also, that circuit breaker you found only has one review.. I've had cheap CB's fail, even had good ones fail but not as fast. I would just be hesitant to buy a CB with one 5 star review and it only cost $10.
    Anathollo likes this.
  8. balakay

    balakay $20 is $20.

    x2 for wiring fridge straight to the battery. I'm wondering if that isn't part of the problems @tex was having with his fridge. I had the same fridge/battery setup as him and never ran into an issue with it wired straight to battery with an inline fuse (never installed an aux fuse block).
  9. tex

    tex Keeper of the 10mm sockets

    I think part of it is my battery and trying to run it on eco mode in a hot truck. Ran great as a garage fridge.
  10. tex

    tex Keeper of the 10mm sockets

    I will see how the Dometic does in a few weeks.
  11. Anathollo

    Anathollo Armorall is my choice of lube Staff Member

    X2 on what @Silverback said.
    I would also recommend just starting out with two fresh brand new batteries. That way if your isolation solenoid fails, the old battery won't be equalizing with the new battery.
    I've heard good things about the North Star series of batteries.
    Last edited: May 17, 2018
  12. CowboyTaco

    CowboyTaco Well-Known Member

    I'm not a fan of cheaping out and having to replace parts, but I'm also not a fan of overspending. There are other less expensive options (example: https://www.amazon.com/Seamander-Bl...Hh&pd_rd_wg=RscSP&refRID=ACQ5WQMXC0X5H27WQ0VN or https://www.amazon.com/Iztoss-Circu...rd_wg=RscSP&psc=1&refRID=ACQ5WQMXC0X5H27WQ0VN), but I have a hard time buying a brand that I've never heard of before. Some of those Amazon brands just seem like the equivalent of an eBay special.

    As for the Circuit Breaker, I'm not set on going that route. So would you recommend going with the ANL fuse instead?

    Better reviewed CBs for similar cost as the example previously used: https://www.amazon.com/ZOOKOTO-Circ...6677&sr=8-19&keywords=100+amp+circuit+breaker & https://www.amazon.com/InstallGear-...76677&sr=8-4&keywords=100+amp+circuit+breaker

    I like the idea of the aux fuse block. I'll probably go that route instead of the inline fuse, though that is an option.

    I picked up the new Duralast AGM Group 35 to replace the starting battery yesterday. The OEM battery has given zero indication that it is nearing end of life. I just wanted to replace it for peace of mind. I want to put a voltage meter on it, so I'll know if it starts to get weak. I may be purchasing the other battery sooner than later.
  13. Silverback

    Silverback I'm not always a dick. Just kidding, go fuck off

    Anathollo and Mauzer like this.
  14. Oswego

    Oswego n00b

    Ill always go this route be it at work or in my personal life. Sometimes you don't even realize you cut corners until they make you bleed lol
    Anathollo likes this.
  15. CowboyTaco

    CowboyTaco Well-Known Member

    Any recommendations/suggestions on the Solenoid w/ VSR?
  16. Silverback

    Silverback I'm not always a dick. Just kidding, go fuck off

    I had a solenoid, never had an issue with it. Very simple concept.. worked as advertised. Switched to a Blue Sea ML-ACR and I like the versatility it has. When the solar is charging the rear battery the ACR will sense that power input and open to allow it to charge both batteries. Unless I turn it off.

    In the 10 years I've had my dual battery and solar setup the only issues I've had where in Arkansas when a 150 amp CB took a crap and the solar charge controller went down in performance for some reason. The ML-ACR worked great.
    Anathollo likes this.
  17. CowboyTaco

    CowboyTaco Well-Known Member

    Yeah, the ML-ACR is really nice and I really like it's feature set. That one would be ideal.
  18. CowboyTaco

    CowboyTaco Well-Known Member

    Ok, so I'm leaning heavily toward using 100A ANL fuses instead of breakers. I will need 3 total: 1 between each battery and the batter isolator, and another between the house battery and the fuse block.

    I'm going to go with the Blue Sea fuse block.

    I'm also leaning heavily toward the WirthCo Battery Doctor 100A Battery Isolator. I really like the ability to jump the starter without needing to run jumper cables.

    4 gauge wire from Starter to Isolator, Isolator to House, and House to Fuse block.

    Anyone want to talk me out of it? Am I missing anything? Can I do better for the money?
    Silverback likes this.
  19. TacoXpo

    TacoXpo TLA

    I use a 200 amp solenoid after 8 years it crapped out. Bought another that has a Stinger label on it.
    Silverback likes this.
  20. TacoXpo

    TacoXpo TLA

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