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Dual Battery Question

Discussion in 'General Tundra Discussion' started by Jrharvey02, Oct 26, 2018.

  1. Oct 26, 2018 at 3:12 PM
    #1
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Hey guys, Long time Toyota owner, first time tundra owner here with a question about the current setup in my truck. The trucks previous owner had most of cartoys installed in the truck over the years (2 amps, 10” sub, alarm, radar detector, compustar dash cam, pioneer avic deck) AND a second battery installed in the covered bed.

    I plan on using this truck and hopefully the second battery for camping and fishing off the grid but when I put a volt meter up to the rear battery (bed) it doesn’t charge with the alternator (truck on). I included a pic of my current set-up, anybody care to explain how the hell these two batteries are “connected” other than the positive wire connecting them, like, how in the hell is this back battery supposed to help the front battery? I’ve included a pic of my set-up from a generic pic off google, if anybody had any info. that’d be appreciated.

    I am pretty familiar with batteries having worked around golf cars for years, but this setup is neither “in-line” or “in parallel” from my knowledge. Both batteries are Toyota brand, but it strikes me weird that if the back battery isn’t being charged by the alternator, why isnt it a deep cycle?

    I almost drained the front battery when I let my kid play in the bed of my truck with the compustar recording her while the truck was off (about an hour of recording) wtf?

    BCA135F9-F468-42B2-8B13-73CD1BF05CC3.jpg
     
  2. Oct 26, 2018 at 3:28 PM
    #2
    Hondoman

    Hondoman New Member

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    I'm puzzled to as to why both aren't being charged, but connecting them together will drain both.

    I have two batteries and an isolator on my sxs. Factory battery runs everything factory, aux battery runs all added accessories. Isolator does just that, isolates the two batteries, but it charges one then the other back and forth. If I drain one battery, it will not drain the other. I dont see why this wouldn't work for you too.

    Here is the isolator I use:
    https://www.amazon.com/True-UTV-SBI-18-Smart-Isolator-UTVs/dp/B00W4QO5F4

    You'll need a beefier version.
     
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  3. Oct 26, 2018 at 3:37 PM
    #3
    Jrharvey02

    Jrharvey02 [OP] New Member

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    So, what puzzles me is the back battery isn’t dead, it’s got a constant state of around 12.32 volts and it’s 2 years old so it must be getting charged somehow? Maybe my truck does have an isolator, I’ve only had a volt meter up to it for a few minutes of testing, how long does it take for yours to transition from the first battery to the second? Is this your setup too, like your two batts are just connected via the positive?
     
  4. Oct 26, 2018 at 3:46 PM
    #4
    Hondoman

    Hondoman New Member

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    It doesnt take long to top off the first battery, then switching over to the second. Maybe less than a minute.

    No, the positives of both batteries connect to the isolator. If they were connected together they will discharge together.
     
  5. Oct 26, 2018 at 4:35 PM
    #5
    bfd300

    bfd300 New Member

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    If one battery is weaker it will drain faster. Plus the battery that is connected to the starter and main batt to the engine will drain faster. Each batter will work as one but need to be isolated during the charging duration so one batt does not overcharge and burn out cells which prob happened in this situation
     
  6. Oct 26, 2018 at 5:25 PM
    #6
    Jrharvey02

    Jrharvey02 [OP] New Member

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    What gives you the impression cells are burned out or something is wrong? I see tons of wiring diagrams online for this configuration, but it’s all for car audio and I’m trying to understand what’s supposed to be happening when the positive of two batteries are connected and an alternator is charging one of the two. Should both batteries be charging when the truck is on?

    I have hooked up my 100 watt solar charger producing 7 amps/hr to the back battery and it charged to 13.7 but the front engine battery showed no increase during the charging, just the normal 12.3 volts. Why are these batteries even connected?
     
    Last edited: Oct 26, 2018
  7. Oct 26, 2018 at 5:36 PM
    #7
    OBXTundra

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    Connecting just the positive is not the issue, so long as the rear battery is also connected to a chassis ground. It does not need a ground ran to the primary battery as well.

    You may have an isolator in place, it has to be getting a charge somehow if it's still north of 12 volts.

    I like auto isolaters, when they work as designed. I really prefer a dual battery switch to give you full control. This is just something you need to remember, but it becomes habit. Dual switches are simple, reliable, and give you more control over your system.

    Leave it on ALL all of the time, turn it to your rear battery when you're off grid, preserve your start battery. Simple. I love dual battery setups. Keep a portable 100w solar panel setup in your rig and you'll be self sufficient. I work with solar a lot at work and also have a panel on my toyhauler and shed.
    perko__8501_dual_battery_switch_3_1.jpg
     
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  8. Oct 26, 2018 at 6:34 PM
    #8
    COTundraRoamer

    COTundraRoamer New Member

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    Just get a Blue Sea Systems ACR and call it a day. Super easy to install, high amperage and bullet proof reliability.
     
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  9. Oct 26, 2018 at 6:47 PM
    #9
    15whtrd

    15whtrd Mr. Blonde

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    To charge both does it need to be in the ALL position? Also if you switch it to OFF is it like disconnecting the battery? Will you loose all settings memory?
     
  10. Oct 26, 2018 at 7:22 PM
    #10
    OBXTundra

    OBXTundra Member

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    Switched to off would be like disconnecting the battery. Just leave it on ALL all of the time. Needs to be on ALL to charge both. Just use it to isolate your secondary battery.

    Leave on ALL all of the time except for when you're using it for camping/accessories, or when you only want to use the 2nd battery. Then switch it to 2, use it for all your off grid and camping stuff. If you run 2 dead, switch it to 1 to start the truck, then switch it to ALL to charge everything back up.
     
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  11. Oct 26, 2018 at 7:26 PM
    #11
    trdprobped17

    trdprobped17 New Member

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    This is what I am using for all the toys on my Tundra. It works very well and provides the level of peace of mind that it’s a proven and tested device. Therefore, it won’t short out and burn up my truck. Quite a few people on the off-roading side of things, use and swear by it. It’s been in my truck for 4 months now and I am super satisfied with it. I have all aftermarket parts that demand more than usual electrical power. From upgraded audio, 6 external cameras, aggressive security alarm system, LoJack, WiFi hotspot, 3 different tuners, ignition timer, remote starter with preprogrammed remote start times, dozens of off-road lights and bars, etc. It works well.

    Genesis Offroad Dual Battery Kit Smart Isolator Toyota Tundra 14-18

    upload_2018-10-26_22-25-40.jpg
     
  12. Oct 26, 2018 at 7:28 PM
    #12
    15whtrd

    15whtrd Mr. Blonde

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    Makes total sense, just like a boat. I love simple! Someday I need to do this.
     
  13. Oct 27, 2018 at 6:04 AM
    #13
    Jrharvey02

    Jrharvey02 [OP] New Member

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    If I were to install one of these isolators would I also need to make sure my electrical loads are all connected to my rear auxiliary battery? I know my compustar dash cam is wired to my main starting battery and I don’t like that at all seeing that it can run while the truck is off and kill the batt. Would an isolator cure that problem or am I looking at having to ensure all accessories are connected to aux. batt for the isolator to function properly?
     
  14. Oct 27, 2018 at 6:34 AM
    #14
    Over the LINE

    Over the LINE New Member

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    Your description makes it sound like there is a disconnect somewhere between the batteries. Otherwise, based on your diagram, both batteries should be basically acting as one. Hidden switch? Blown fuse?

    As far as wiring for off grid use, I am not a fan of "1 + 2 + both" switches. It's easier than you think to forget and drain your engine battery with accessories. A combiner/isolator with all accessories tied to the "house" battery is a much safer setup.
     
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  15. Oct 27, 2018 at 7:37 AM
    #15
    COTundraRoamer

    COTundraRoamer New Member

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    You could do it either way. You could run stuff off your main which is a little unusual and run your second battery as your start battery.
     
  16. Oct 27, 2018 at 8:33 AM
    #16
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Good call, to make sure the fuse was working I disconnected the wires going to the back battery (bed) and tested the WIRES, they came in at 12.11V. I tested the front (engine) battery and it’s at 12.11V, great, power is making its way from the engine batt to the rear batt. BUT when I hook the rear wires up to the rear battery and start the truck I get 13.87V at the battery in front (engine) and 12.37V at the back (bed) battery. Then to throw another kink in to this scenario, I switched on my bed LED strips which are hardwired into the back (bed) battery and can slowly watch the voltage drip from 12.37 to 12.30 to 12.29 to 12.28 and so on, while the truck is running and all the wires are hooked up. If this back battery was getting charged by the alternator, I shouldn’t be losing voltage from 2 LED strips and I’d assume I should be getting the same reading on the front battery (13.87) as the back (12.27) with truck and alternator ON. Wtf is going on? I can verify power up to the wires in the truck bed but once they get placed onto the batt, it’s like something stops working...?

    B7871557-13AA-4457-95EF-5F71C79D3028.jpg
     
  17. Oct 27, 2018 at 8:43 AM
    #17
    Over the LINE

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    Bad ground on rear battery? If LED strips are connected directly to AUX battery negative they would still work.
     
  18. Oct 27, 2018 at 8:47 AM
    #18
    Jrharvey02

    Jrharvey02 [OP] New Member

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    They do still work, always have. But when I turn them on, I can watch the voltage on the battery drop every couple seconds from 12.30 to 12.29 and so on. This is all while the truck is on and supposed to be charging the back battery, why is that back battery showing 12.30 and falling with the led strips on when the front is at 13.87 being charged by the alternator.
     
  19. Oct 27, 2018 at 8:53 AM
    #19
    Over the LINE

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    My question is, does the rear battery have a bad ground? A bad ground would mean the front and rear batteries are not connected and therefore would cause the situation you describe.
     
  20. Oct 27, 2018 at 10:24 AM
    #20
    Jrharvey02

    Jrharvey02 [OP] New Member

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    I see, it’s grounded with 2 separate 4(?) gauge wires directly to the chassis near the rear wheel. It looks okay, but is there a way to actually the test to be certain it’s grounded properly?
     
  21. Oct 27, 2018 at 11:00 AM
    #21
    Hondoman

    Hondoman New Member

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    If you have a multimeter you can check the resistance between the negative terminal and a known good ground like the frame, body etc...

    If it is open or a high value the ground connection is not good.
     
  22. Oct 27, 2018 at 11:24 PM
    #22
    computeruser6

    computeruser6 Climate heretic

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    The dash camera would take a very long time to drain your battery; I wouldn't really worry about that too much. Are both batteries approximately the same age? I would also recommend swapping out this big fuses for breakers as it will make isolation much simpler and shutting a breaker is much simpler than replacing a fuse.
     
  23. Oct 28, 2018 at 1:07 AM
    #23
    Inquiringone

    Inquiringone -Blue N Blac- an a little chrome

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    U can take the guy out of the garage, But U can’t take the garage out of the guy
    Not many yet, mostly stock.
    Did you un bolt the grounds and clean the terminals and landing spot re-bolt up? then re check.?
     
  24. Oct 28, 2018 at 5:15 AM
    #24
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Yup and that was the issue, bad ground.
     
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  25. Oct 28, 2018 at 5:25 AM
    #25
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Both bats are same age - about 2 years old. The dash cam was draining my batt in a very short time, but I’m hoping that was because the back battery was not grounded properly.
     
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  26. Oct 28, 2018 at 5:26 AM
    #26
    Inquiringone

    Inquiringone -Blue N Blac- an a little chrome

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    U can take the guy out of the garage, But U can’t take the garage out of the guy
    Not many yet, mostly stock.
    Good times, glad you found out the issue. I've had ground problems in the past with electrical systems. Come to find out the landing spot was corroded and hidden from eye site by the wire lugs. :thumbsup:
     
  27. Oct 28, 2018 at 6:09 AM
    #27
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Wasn’t even that corroded, Colorado is good about that. It was laziness. Cartoys didn’t bother to sand frame before slapping the grounds onto an existing bolt in the frame. This also fixed my subwoofer sound issues, shoulda known...
     
  28. Oct 28, 2018 at 7:18 AM
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    Over the LINE

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    Glad I could help.
     
  29. Oct 28, 2018 at 8:01 AM
    #29
    Jrharvey02

    Jrharvey02 [OP] New Member

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    Thanks for all your help guys
     
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  30. Jul 9, 2019 at 2:47 PM
    #30
    Detour

    Detour New Member

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    Great topic! I’m a long time tundra owner but I don’t do any mods on my truck, so where should I go to have duel batteries installed? RV shops? Any suggestions appreciated. Thanks?
     

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