How to Add a Second Battery to your Truck.

Discussion in 'GM Electrical Tech' started by Springthing, Mar 13, 2009.

  1. Springthing

    Springthing Epic Member 5+ Years 1000 Posts

    Here was my issue: I am about to work on a sound system for the Suburban. One part of the system is an amp that needs a 4g power lead wire, directly from the battery to the amp. The problem was that the battery already had two rather thick wires to it already; an additional one would have crowded the area. Not to mention the fact that I was wondering what kind of draw was already coming off this one battery!

    So... I decided to put in a second battery. The suburban was designed for a second battery so this should be (and was) a piece of cake!

    Here now, I present you with what had to be done to install a second battery. I hope this write-up serves someone else well in the future.

    As usual I make it known that I NOT an expert and anything written here is meant as a guide only. Please do your own homework - I can't be held responsible for anything you do to your equipment. If you end up blowing up your truck/car, catching the garage on fire that lights your house ablaze and you happen to lose your beloved chihuahua in the ordeal well, that's your tough luck!


    Far (passenger) side is the current battery. You can see on the driver's side (forefront) the battery tray for a second battery.

    After checking sticker codes I determined that I had the 140amp alternator which is the alternator installed for two-battery setups. Perfect!
    Last edited: Mar 14, 2009
  2. Springthing

    Springthing Epic Member 5+ Years 1000 Posts

    On the passenger side, front, of the truck you will find the power distribution block. This is the place your new battery much be connected to. This safely puts the battery in parallel with the other. Of course you know that adding a new battery in line with the other would give you 24v and you'd never do that and know exactly what all this means or you'd not even be attempting to do your own electrical work on your vehicle, right? Good. The distribution block splits the alternator power to both batteries and sets them up, as mentioned, in parallel.


    Pull the plastic cap off and cut the zip tie that holds it there. You will need to remove it in order to cut a gap in it.

    Remove the nut on the bolt which you will be adding your (+) wire to and fasten the new (+) tightly in place.


    With the plastic cap off, cut out a notch for the new (+) wire to pass through. Make sure you have no sharp edges left - give it a quick pass with a piece of sand paper or file.


    Reinstall the cap, replace the cut zip tie through the eyelets. (visible in the above picture)
    Last edited: Mar 14, 2009
  3. Springthing

    Springthing Epic Member 5+ Years 1000 Posts

    Now you need to find a good ground. Find a big honking bolt somewhere in the vicinity of the new battery. I choose a bolt off the engine.

    *** if you happen to pick a spot off the block leave enough slack in your ground wire to ensure enough room for it to move when the engine moves! ***

    Here you see the ground wire in place. Follow the unshielded end of the wire resting on the battery to the block...


    Because I wanted maximum free-flow of power I chose to install posts and use big ol' post terminals as opposed to screwing on the leads to the battery. This assured me the utmost minimal power-loss, if any, and left room to add the 4 gauge wire running to the amp in the near future.


    All that was left was to run the (+) wire to the battery from the distribution block, putting on the terminal to screw to the side post, and shielding the wire itself. Here we see the wire, shielded, running from the passenger side to the driver's side, hooked up to the new battery.


    That's it, folks! Simple and straight forward.

    A couple of key notes:

    Side post only! Top post will hit the hood and not let you be able to close it! **see next post for update**
    If you aren't 100% sure of what you are doing - don't! Let a professional do it for you. Minimal cost.
    As usual when playing with a car battery - plug and unplug the (-) lead first!
    Verify your alternator is adequately sized for two batteries.
    Say no to drugs.
    Always put your best foot forward.
    There's no I in team.
    Quitters nev-....

    ..ok, too much!

    Hope this helps someone in the future!
    Last edited: Mar 14, 2009
  4. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts


    That sucks that you don't have room for the top posts, boy that makes me glad that I don't have a truck like that......Just kidding! I had room to mount all of my crap on top of the battery, and then I even mounted three transformers on top of my fuse box and it still doesn't hit with the stock hood. The only reason I said anything is for all the Silverado people out there wondering if they have room, I am 99.99% sure you do have room. Great job with the install Springthing, that looks really clean the way you installed it too.

    BTW I have the regular hood, not the power dome or the HD hood.
  5. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    A couple thoughts to keep in mind... Theoretically, if you do not use any type of battery isolator system, and even if you do, you want to try to keep your two batteries of the same model and preferably batch made in the factory. The reasoning behind this is that if one battery gets discharged more than the other, the battery that is better off will attempt to charge the lower battery which will cause the good battery to die too. Like I said, this is less important in an isolated environment, but almost essential in a straight-parallelled environment. Another cool reason to have an isolator is that in an emergency, the second battery can act like an onboard jumpstart. I'm still running a single battery, but once I get everything set up, I will be running an isolated setup with 2 optima yellow tops for my cranking batteries with 2 optima blue tops as my accessories batteries. In that setup, the 2 banks of batteries will have the batteries within the banks tied together all the time, but those batteries will be identical batteries bought from the same batch. Should be great, but expensive and heavy. :gasp:
  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Thanks for taking the time to document this modification! Great job.
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Something for those that already have a GM installed dual battery system:
    It hooks-up and looks exactly like the above installed system, but theres an isolator in the system and for some reason if your main battery is bad the isolator wont allow you to jump from the good aux battery to the bad one to start the truck. You have to use a battery not connected to the system.

    This may be something peculiar to 97 model trucks (I never researched further).
    If your ever stuck with a bad battery just swap the batteries or disconnect the aux from the system and then use it to jump start. The system will run without 2 batteries.
    And to further confuse you the system wont start the truck with a dead aux battery, it must be jumped from an outside battery or disconnected if its dead.

    I solved this problem by bypassing the factory isolator and installing one from Autozone, it doesnt change the operation of the system except for the ability to jump with your aux battery or start the truck if the aux battery is dead.
  8. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    How to -Adding a second battery to your truck

    GM used to have a bolt in dual battery kit for 96-99 trucks avalable from GM parts.
  9. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    They still do, over the counter cost is around $340, depending on dealer.
    The over the counter kit comes with a battery.
    Aftermarket can run as low as $150 depending on battery used.
  10. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    It seems like among the off-road community, at least the ones I have seen so far, Hellroaring isolators are the most reccommended and best in the business for battery isolation.

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