Dual Battery Setup on My Silverado for Camp Power

Important Update:Β Make sure to connect the negative terminals of the two batteries. Grounding to the frame for the accessory battery will not excite the hal-effect (current) sensor, which is located on the negative terminal between the starting battery and alternator on the truck.

Not making this connection will lead to both batteries undercharging, especially in warmer weather or longer trips. Failure to make this connection will cause premature failure of the batteries, potential dead starting batteries, and repeated undercharging.Β You have been warned.

New Battery Graph

Since 2004, I have always run a power inverter off my truck, that converts 12 volt DC power into 120 volt household power. I use it extensively through the summer season to provide light and power to camp for small appliances like my alarm clock, laptop, and electric lighting. Electric lighting really beats any other camp lighting.

Sparkle

My current set up uses a Vector-brand 800-watt Power Inverter, connected to a second battery, that is disconnected from the starting battery when the engine is off. There is no danger of a dead starting battery as the second battery is disconnected from starting battery when the truck is off. Once the truck is turned on, the isolator relay reconnects the second battery to the alternator.

Hidden Battery Inverter

As long as you don’t drop the battery below 11.3 volts β€” where the inverter automatically turns off due to low voltage, you will have constant 120 volt output. As the isolator does not kick in until the alternator is spinning, there is no voltage drop when the engine is cranking.

Battery Isolator

When I got my 2011 Chevrolet Silverado to replace my old pickup, I was quite happy to discover that all full-size pickups come with dual battery locations, and at least with All-Star Edition Silverado, all of the hardware for installing a second battery exists (second battery tray, high-output 145 amp alternator), except for the $5 tie down and the wiring.

Equipment Used and Costs.

The installation would have cost me a total of around $475, although $75 of it was the inverter I had already purchased years ago and have moved on over my old truck.

  • Vector 800-watt Power Inverter – $75 – Pepboys (probably less now)
  • Walmart 24DC-6 Marine Battery (101 amp/hr) – $79 – Walmart
  • GM OEM Battery Tie Down Block – $4 – DePaula Chevy Parts Store
  • GM OEM Battery Tie Down Bolt – $1 – DePaula Chevy Parts Store
  • Pacific Automotive Corporation 200-amp Battery Isolator (Large Mechanical Relay) – $65 – Boomer McCloud
  • Wire, Conduit, Connectors, Fuse Tap – $80 – Boomer-McLoud

The parts total was $305. Not too bad. If were to install it all myself, it would have required additional tools like a battery cable crimp, plastic molding puller, sealants, which if you don’t own such tools and parts would add costs. In addition, you would have to buy extra parts in packages you wouldn’t neccessarly use. That proaly would add up to close to $150, plus your time isn’t free.

I had Boomer-McCloud, on Central Ave in Albany, a chain automobile electronics/car audio wiring store, do all the wiring, install the isolator and assorted related parts. They did it in two hours of labor, which cost $150. While the wiring is not rocket science, having it professionally done, increased the quality over what it would have been done had I done it myself. I am not a wiring expert, even if I know how electrons flow.

What I Had To Do.

Boomer-McLoud did all of the wiring and installation, although I had to purchase the battery and tie down, and also provide the battery inverter.

I decided to get a Walmart Everstart 24DC-6 Marine Battery, which is a dual purpose battery for starting and deep cycle. Walmart Everstart batteries are pretty good quality for the price, they are manufactured by Johnson Controls in the USA. I would have gotten a true deep-cycle, but I was on a budget, and finding something that would fit in the battery tray was a bit of a challenge. I figured if going to take some abuse β€” occassionally being overly deep cycled β€” I might as well not spend a fortune.

Second Battery (Marine) for Powering Inverter

The Walmart Everstart 24DC-6 Marine Battery fit perfectly in the tray without sliding or being oversized, although is slightly taller then the standard Group 48 battery. It has a 101 amp/hr rating, which is sufficent power for at least a day’s worth of camp compact florescent lighting and small appliances like an alarm clock, cellphone chargers, etc. If battery gets too low, you just fire up the truck and charge it up.

Then I went to DePaula Chevrolet’s Parts Department and picked up a battery tie down. You just want the tie down plate and battery bolt. It’s like $5 for both of those parts. I then had to install the battery myself, and tie it down. You will need several long socket extensions to reach below the battery to install the tie down bolt. Once it’s installed, the battery is very secure, just like the factory battery.

Then I had to make an appointment with Boomer-McLoud, and explain what I wanted to do. They had some questions, and I showed them where I wanted the inverter mounted, and they did the rest. I just dropped it off before work one day, then picked it up later in the afternoon. Paid $315 with tax. Hit the switch on the inverter, plugged in electronics, and I was off.

Pictures of Individual Components.

This is the second battery, with the isolator mounted close to it.

Second Battery (Marine) for Powering Inverter

The isolator is like a giant electro-mechanical switch or relay, that is closed or “excited” by a small amount of current that causes the relay to shut. It is excited by a fuse tap in the Throttle Position Sensor Fuse from the main power bus. In the background is the main fuse bus, with the top off it.

Fuse Tap from Throttle Position Sensor to Excite Battery Isolator Relay

Rather then mess with any factory wiring, the main feed wire comes off of the main (starting) battery terminal. Notice the 150 amp fuse for safety. You don’t want a shorted wire to equal a fire.

Starting Battery 1

Fuse Holder and Connection off Starting Battery

Here are the fuses and other wires coming off the second (inverter battery).

Second (Inverter) Battery, Battery Isolator (Relay), Second Fuse Tap

And finally, the power feed to the second battery, runs right on top of the main power bus from the Main Power Bus Distribution Box, just like how Chevy does it with the factory second battery install.

Wire Running To Second Battery

I’ve only used this set up for a couple of nights, but appears to work real well. The starting battery never gets low, the camp power works well all night long. you can easily plug in heavier loads like my 90-watt laptop adapter, and there is no dimming of headlines or sign of stress on the alternator.

I hope this is helpful. Please feel free to email me with any questions. β€” Andy

89 Comments

  • ken ragan says:

    I want to do the same thing and mount the inverter on the floor of the cab under the radio area……is there an easy way to put the wires through the firewall? Thanks…Ken Ragan

    • Andy Arthur says:

      Yes, near where the steering wheel column rod comes through, there is a plastic-leather portal were a number of wires come through. There is a lot of extra room there. Carefully cut the plastic, and you can run any number of wires there. Just make sure to seal it up well when done.

  • ken ragan says:

    Why does your main power tap into your other battery instead of just tapping into the back of the alternator? It seems you used a lot of extra wire and will probably stress your main battery. My alternator output screw has plenty of room for an extra wire and it is close to my new battery……should I not tap it there?

    • Andy Arthur says:

      Either place should work. The benefit to connecting to the battery terminal is GM left an extra terminal up there to connect a wire to the second battery, and it’s easy to get to, but you can connect it directly to alternator directly (there is no advantage to doing this except a slightly shorter run of wire and therefore less line drop).

  • ken ragan says:

    Where did they run the battery negative wire to?

  • Steve W says:

    I have a 2011 Silverado also and I am wiring my setup almost identical. Can you tell me what the fuse number is according to the diagram on the fuse box lid that the wiretap is on? And, have you had any issues yet with this setup?

    Thanks.

    • Andy Arthur says:

      I will have to take a look tomorrow when the sun is up.

    • Jesus Mendez says:

      Oh i get it! So instead of just running a ground wire from the auxiliary battery to a place on the frame nearby, you actually have to take the ground wire from the auxiliary battery and run it all the way back to the negative terminal on the primary battery that way the hall effect sensor can read the current on both batteries and can adjust.

  • tom says:

    everybody want to spend all this $$ and put all this stuff. not needed. simply put ” u r battery is a 6 cell, turn it into a 12 cell ” problem solved. use parallel wiring and hook the red to to red and the black to to black.

    • Andy Arthur says:

      Paralleling the two batteries is good, if you want to use them with a plow or other heavy electric load when the engine is running. The problem is when the engine is turned off, and your using an electric load, it will discharge both batteries, when in parallel — granted it will take twice as long to discharge both batteries.

      I wanted to be able drain one battery down, for camp power, and still have a fully charged starting battery, so not to get stranded in the wilderness with a dead starting battery. I accidentially discharged my starting battery on my old truck once, and had to roll start it (manually transmission). I also had a “hot-shot” jump pack, but that didn’t always work when the battery was fully discharged.

      • Ron Forney says:

        I had a question I was considering doing the parallel battery set up because I am pulling a lot of power due to winch stero 52 inch light bar CB etc etc but I also camp and use a lot of acc will this setup accommodate both needs or do I need to choose between the 2 thx great article

        • Paul says:

          Hi Ron,

          The setup with the isolator would be great for you because both batteries are connected together while the truck is running allowing you all the apps from both batteries for your stuff. When you shut off the truck, the isolator shuts off and then the stuff on the extra battery can be used without draining your starting battery. Hope this helped.

      • Jack says:

        I like your set up. A cheaper and less convenient option is a knife switch. You can disconnect when camping and reconnect it when running your engine. It’s a poor man battery isolator.

        I did that as a temporary repair on my motorhome 3 years ago. I still haven’t got around to fixing it properly.

  • steve says:

    I ended up getting power for the PAC from the ign/acc fuse. works great. It has power during cranking so the PAC isn’t clicking on and off when you start the truck. I do get big swings on my Volt gage though. I’ll have to look into that further. Other than that, everything else works good.

    • Andy Arthur says:

      The big voltage swings may be normal, if they occur over time when driving, especially when hot out.

      http://www.chevytalk.org/fusionbb/showtopic.php?tid/186067/

      My truck goes from a low of 11.7 volts in 100 degrees weather to 15.3 volts, when it’s below zero, and one or both of the batteries is low, with headlights and defrost on. 14.1-14.3 is about normal, in temperate weather. This not only prolongs the batteries, but also reduces fuel economy, by reducing the drag of the alternator by reducing the field current.

      The second battery will somewhat increase the swing, because the alternator is more likely to see the batteries as overcharged or undercharged.

      I wouldn’t worry about.

  • Stacaz says:

    How would the following information affect adding an Aux battery to the system

    http://www.justanswer.com/chevy/6u8az-chevrolet-silverado-1500-does-charging-system-work.html

    It discusses how the Silverado 1500 Electrical Power Management system automatically adjusts the output of the alternator to determine best rate of charge for the battery’s current State of Charge. It even has a amp-meter in line with the Neg main battery cable. I did not know that vehicles even had such “smart” charging systems these days, like the 3-stage chargers you can get for RV battery banks.

    I assume adding a second aux battery solenoid isolator would confuse the EPM, when it automatically switches the Aux battery in and out of the loop during starting, running, etc.

    I ordered one of these to install in my 2012 Silverado 1500. I assume no major problems, but what effect will it have on the EPMs algorithm for best charging and long life of BOTH batteries?

    Thanks.

    • Andy says:

      Correct, you can’t use a diode-based isolator with a modern vehicle with a voltage-regulator, or the regulator will get confused and will either undercharge or overcharge the battery (and the alternator light will stay on). You can use a specialty diode-based isolator, designed for a GM vehicle, that has an extra voltage “sense” terminal, which you run back to the voltage regulator inside the alternator to provide it charging information.

      That said, having talked to the local shop, I just went for a standard relay-based isolator (200 amp) like the Stringer 200 AMP or the PAC 200 isolator (the later I used). They are low-cost, and pretty durable. They are a simple mechanical switch that connects the two batteries when a voltage is sensed on the third terminal. I use a fuse tap to get a voltage from the Throttle Position Sensor Fuse.

      http://www.amazon.com/PAC-PAC-200-200-Power-Relay/dp/B000CEBXRS

      The “smart” relay-based isolator sounds interesting, but I would argue it’s overkill on a truck with a fairly large alternator to start out with. The voltage regulator will step up the voltage up to 15.1 volts on heavy electrical load in cold weather.

      • Stacaz says:

        Thanks for posting the pictures of the great cabling job, looks better than OEM. I plan to do mine myself. The charging does not depend so much on the voltage regulator(s) on the alternator. They are controlled by the EPM, which senses all sorts of other things about battery condition based on past use, current use, with a software algorithm. It assumes you have only have the starting battery in the loop. When you add the second battery, you basically double the available capacity (amp-hours). This might confuse the EPM, since it assumes a lower capacity in its algorithm. The earlier posts about the dashboard voltage indicator swinging around might be due to the EPM’s confusion over whether the battery “bank” is charged, half way down, discharged, etc. I don’t think this will pose a major problem, but, like you said, might lower the efficiency of the charging system with regard to gas mileage. Might have to put in an extra gallon or two per year. Maybe there is a way to “tell” the EPM that the capacity has changed, via reprogramming. Will have to consult GM engineers/techs on that one…

        • Andy says:

          Interesting. That’s good to know. I had to move the car radio back onto the starting battery, as I had problems with the accessory battery charging if the starting battery was fully charged. Thanks for the info.

          • Stacaz says:

            That’s why I went with this isolator: http://www.colehersee.com/home/item/cat/211/48530/

            It automatically connects and disconnects the aux battery to the main battery according to voltage readings on each battery. It waits until your starting battery has a good charge on it before it connects the aux battery for charging. You mentioned it was “overkill” in an earlier post, but I think those benefits outweigh the increased cost. You never have to think about it. After you stop the engine, it will wait until one of the batteries drops below about 12.7 volts before it disconnects them. I also wired a dash switch that let’s me connect the aux battery in case the main batt dies, and I need to start the truck. It will leave them connected for 1 minute. That’s enough time for the good aux battery to bring the main battery charge up enough to start the truck. That’s the main reason I installed this. Living in the desert heat of Arizona, batteries often die without notice. I hate the thought of being out in the middle of nowhere, hunting or riding quads, and suddenly I can’t start my truck to get home! I think the delay that this “automated” isolator offers would benefit your setup as well. Will send pics after I am done.

          • Stacaz says:

            If you are running your aux battery all night and discharging it fully, I would add an automatic disconnect to that battery, so it cuts it off BEFORE it’s fully discharged. They have those on that site in previous post. It will also serve the purpose of prolonging the life of the aux battery.

          • Stacaz says:

            If you run down your Aux battery, AND your starting battery suddenly dies without warning, what are you going to do? Thus, the need for auto-disconnect on your Aux battery. At least you will have something left to start the truck…

  • Stacaz says:

    Actually, this is the auto isolator I am installing: http://www.hardworkingtrucks.com/gm-1500-dual-battery-install/?pg=2

  • jonnyk says:

    What size wire was used between the two batteries?

  • Stacaz says:

    I just posted the following question to justanswer.com and paid $24 for an answer (the Chevy guys there are really good, but I only found basic knowledge of the standard EPM prior). Do a search there to see when it shows up…Cheers!

    Hi, I added an Aux battery to my 2012 Silverado 1500 according the plans here:

    http://www.hardworkingtrucks.com/gm-1500-dual-battery-install/?pg=2

    Many people have probably done this as well. I read your link about How the charging system works, and have some questions for you. How does the EPM react when there is suddenly about twice the amp-hour capacity added to the system? I understand there is a HAL Effect sensor on the Neg terminal of the main battery. Mine is wired according to the site above, as many others have, although plugged straight into the IGN+ tap with a simple isolator.

    I have put together several battery “bank” systems for RVs that included 4-stage “smart” chargers, which seems to be how the new GM trucks have been configured, in order to give longer life to the battery as well as improved gas mileage.

    Would you suggest connecting the Neg terminals of the main and aux batteries so that they go exclusively through the current sensor for the truck? How would adding the aux battery, in general, best be wired, according to the programming in the EPM, which seems to assume there is only one battery connected? Will it be “fooled” by adding the second battery, and how so? What are the consequences, and best practices?

    Thanks.

    Country: United States
    Make: Chevrolet
    Model: Silverado 1500 Classic LT
    Engine: 5.3

    Already Tried:
    No sites or forums via Google have provided any satisfactory answer.

    • Andy says:

      Within the next month, I will be adding a solar charger and a 100-watt solar panel. This will keep my inverter and CB radio powered throughout the day, without having to start the truck occasionally. It also should keep the truck’s AM/FM/CD player working so I can listen to music at camp.

      When I do that, I will change the fuse tap from the throttle sensor position fuse, to one that is hot when the key is turned to accessory or the engine is on. This way I can charge both the starting and accessory batteries from solar panel when hanging out in camp during the day-time, and better keep the batteries balanced. When the key is off, the batteries will be isolated like before.

      I am just waiting on the panel and have to do some wiring. The panel will be mounted on plywood rather then the cap, so I can move it were it’s sunny.

      • Stacaz says:

        You can tap fuse #43, with an add-a-fuse at least on the 2012 Silverado 1500 LT for Ignition V+. That’s what I did to power the relay that let’s my second voltage gauge read the aux battery separately from the main one, at least before the auto-isolator kicks in and both batteries are connected and the gauges read the same. You can remove my earlier post concerning Justanswer.com. They suck. Could not answer my question. Sorry about that. Should have known…bunch of hack mechanics….

        I had solar on my old popup camper, Starcraft 13RT. You’ll just need circuitry that doesn’t allow it to overcharge the batteries, or at least get an auto-watering system, like I had on my 6-volt battery bank, in series for 12v. Once you get into all this, you’ll need more advanced knowledge of 12 lead-acid battery systems and the best ways to keep them at peak performance. I’ve also done battery systems on boats involving banks of over 12 high-end AGM batteries.. Email me for more discussion. stacaz822@yahoo.com. I have over 10 years experience with all RV systems, and 20 years with electrical and software engineering. I really appreciate your blog here! πŸ˜‰

        • Andy says:

          Thank you, that’s very helpful. Now I won’t have to search for a switched fuse. I wired up the solar controller this past weekend. The solar controller’s load circuit is wired to power the CB radio, so I can leave the CB radio on when camping and it will only power down on low voltage.

          I will post pictures along with writing an article once everything is finished.

  • john says:

    Or you can just buy an inexpensive adapter and plug your inverter directly into your 7 pin trailer connection and simply rely on the vehicles built in battery drawdown protection. Ez peasey

    • Andy says:

      That will work, but your limited on the load, as I doubt the accessory wire to the trailer pin is wired for much more then 10-20 amp 12 VDC. That’s only 100-200 watts of power. My inverter is rated for 800 watts, although I usually only use a fraction of that power.

      I also am not sure if the accessory wire is switched by battery drawdown protection, if it is, that’s good. One time though, I got in trouble with the battery drawdown protection — it switches the radio off, but does not downpower the computer, so even if after the “Battery Low: Start Vehicle Now” message comes on, if you don’t turn the key on right away, you’ll have a dead battery in 15-20 minutes.

      Another advantage of the second battery, is you have much more reserve capacity. I can run the deep-cycle battery down quite low, until it finally shuts off.

  • Levi says:

    I was wondering, why you used one 150 amp fuse and one 80 amp fuse?

    • Andy says:

      I think it’s actually a 120 amp fuse and a 80 amp. I probably wrote the article wrong.

      The inverter can pull about 70 amps (800 watts / 12 volts = 66 amps with a slightly higher draw for overhead), and the alternator can put out 150 amps, with power going to the battery and the inverter.

      • Michael says:

        I’m confused… The fuse pictured coming off of the starting battery is an AGU style fuse, which to my knowledge don’t come any bigger than 80 amp. Can you clarify?

  • Joshua Reindl says:

    Did they run a ground wire all the way across the engine like the power wire or did you just go from your aux battery to the engine block?

    • Andy says:

      I learned the hard way it’s important to connect the aux battery ground to the starter battery ground terminal. Between the starting battery ground and the frame there is a hal effect current sensor. This tells truck’s voltage regulator to kick up the voltage up when the battery is discharged. Unless you connect the battery grounds together, you will:

      1) Fine your auxiliary battery is totally discharged or mostly discharged without warning. The voltage regulator will cut alternator voltage to near zero output if it thinks the starting battery is fully charged.

      2) You won’t be able to charge the auxiliary battery unless the starting battery is discharged.

      3) Under charging will kill both the starting and auxiliary battery prematurely.

      So connect both ground terminal together. ☺

      • robert howard says:

        SO YOUR SAYING CONECT GROUNDS OF BOTH BATTERYS AT THE POINT ON THE STARTING BATTERY OF TRUCK ?I HAVE 2017 SIVERADO? THANK YOU FOR THIS GREAT INFOTRYING TO CAMP OUT OF TRUCK OR I HAVE BEEN AND I USED A PORTABLE BATTERY BUT ITS NOT GOING TO BE ENOUGH POWEER FOR 12 VOLT FRIDGE AND DIESEL HEATER.

  • Michael says:

    This may be a stupid question I don’t know. I want to install a second battery also but its only going to be used on rare occasions so say I’m driving down the road and the second battery has no load on it will it get overcharged? Like when I plug a battery charger to the battery when the battery gets full the charger turns off, what is there to turn off the current to the battery once it’s at a full charge? does that make sense

    • Andy says:

      You don’t have to worry about overcharging either battery, as the battery charges will equalize while connected. The alternator will automatically cut the voltage when the battery is charged to prevent overcharging — based on the amperage demand as sensed on the negative line.

      However, make sure to connect the negative terminals on both batteries to the factory negative line going back to the block. This is important, as there is a hall effect sensor on the negative line, that tells the voltage regulator on how much voltage to put out based on the amount of current flowing into the battery.

  • Jon combs says:

    Is there a inline fuse fuse just between the two batteries? Not between the marine battery to the power inverter?

  • John says:

    Ive got a question,
    Ive got a 01 e350 shuttle bus that ive recently hooked up a 750 watt inverter to run a tv and game sytem for kids and to watch movies on long trips.
    I have an issue where the inverter rins for about 40 mins, then shuts iff due to high input. I just realized that i have a ho output 200 amp alternator that im assuming is shutting the inverter down.
    My question is what can i do/use to drop the amps to my power supply in order to run the inverter?
    The bus has a slide out compartment where a battery was located to run a wheelchair lift, compartment has battery cables still inside, that where i ran all my power from. Also i added several cigarette lighter/ power inputs that also feed off this cable inside the battery compartment.
    Any input would be greatly appreciated, thanks.

    • Andy says:

      I don’t think it’s the alternator causing the inverter to shut down. The inverter will only use the amperage it needs. I think the issue is you either have a defective inverter, or you have too much load on it. Maybe the inverter is getting to hot from the heat?

  • Wade says:

    I believe I have the same setup as you do in my Silverado with the extra battery compartment. Setup is similar to my old Class C with starting and house battery. With this setup could I also use (when in camp a while) a battery charger to the house battery and generator so I don’t have to start up the truck?

  • Jahir says:

    Hi
    I am trying to disconnect the main electrical loads from starter battery and connect to the auxiliary battery. However it seems difficult as its complicated circuiting with dynamo. Pls help suggesting isolating it on toyota Landcruiser.

  • Davidj281 says:

    HI, in one of your pictures on the 2nd battery you have a fuse coming off of the power. What brand is this and where does this line go?

  • Joe says:

    Do I need to run the auxillary battery ground cable through the Hal-effect sensor, or just to the start battery ground?

  • Randy says:

    I have a chevy Silverado 2007 4.8 vortex.I want to add 4 deep cell batteries to my truck.For long use without having to start the truck.please tell me what isolator to use.And is it ok to put the batteries in the back floor board of the cab.So I have more camping space in the bed.

  • Mike says:

    Andy, Once the Aux battery needs charging and is being charged by the alternator, what is your charging voltage from the alternator (gauge reading)? Does it fully charge the aux battery or does the alternator drop down the voltage prematurely. My Aux battery is grounded through the frame. My alternator prematurely drops voltage and I either put the headlights on or press tow/haul to get higher towing voltage. It still is only about 14V which is not enough. I have a manual solenoid system for isolation. I have used the system for 5 years to charge my truck camper. Just trying to get more voltage for a faster more complete charge.
    Thx

    • Johnny says:

      So I haven’t set this up yet, but I just read one of Andy’s replies and it answers your question.

      I learned the hard way it’s important to connect the aux battery ground to the starter battery ground terminal. Between the starting battery ground and the frame there is a hal effect current sensor. This tells truck’s voltage regulator to kick up the voltage up when the battery is discharged. Unless you connect the battery grounds together, you will:

      1) Fine your auxiliary battery is totally discharged or mostly discharged without warning. The voltage regulator will cut alternator voltage to near zero output if it thinks the starting battery is fully charged.

      2) You won’t be able to charge the auxiliary battery unless the starting battery is discharged.

      3) Under charging will kill both the starting and auxiliary battery prematurely.

      So connect both ground terminal together. ☺

      • Andy says:

        Yes, that is correct. Thanks for explaining that so clearly!

        I also suggest adding a solar panel to your truck cap — this gentle charge of solar really helps ensure a good full charge on your deep cycle.

  • Jesus Mendez says:

    I have a question about the small ground wire that comes from the auxiliary battery does that have to go all the way back around to the negative terminal on the primary terminal??

  • Bret Hart says:

    At the starting battery is it safe to bolt the secondary battery’s positive cable to Smart Isolator on top of the main bus and alternator cables utilizing the existing 175A GM Littlefuse when utilizing a second 175A Littlefuse at the secondary battery?

  • Steve Livni says:

    Im having start run issues after installing a isolator code ran that it was a o2 sensor bank 2 I changed that out still , after I was done she ran fine about 20 minutes I shut her down and then she started idling rough slowing down and dies I unhooked the two wires to the isolator and still having problems with the stalling and I can’t figure out what it is

    • Andy says:

      You are missing the second fuse in the fuse tap.

      • Brad says:

        Hi Andy, do you have any pictures of how you did the ground wire/cable? If connecting the AUX batt gnd cable back to the starter batt gnd, do you go up through the sensor and then onto the batt post or just to the batt post directly? Als0, where do you put the small gnd wire you mentioned and what ga wire is it? Thanks!

  • Justin says:

    Hello. Thank you for posting the information. I have a question. I set mine up virtually the same way yours is in the diagram at the very top. With the exception possibly of where the fuse tap is located. I am using a stinger 200 amp isolator. When the car is running however why is both batteries charging simultaneously as indicated by the multi me to read out but the elevated voltage from the alternator?

  • Jay says:

    Hello, and I am not good at monitoring posts, but I need some advice with the 2017 Silverado, dual batt setup w/12V 140 Amp Dual Battery Isolator. Both stay charged as configured but the issue is the Cameras that I installed are designed to have direct current for motion, record, when bumped, parked, etc. After about 7 days of not drive during this Pandemic. Yup, you guessed it, dead main battery! I could easily switch the camera over to the second batt, but my question is, how can I configure the setup to have the second battery to assist with starting the truck in these situations?

    Standard configured Positive from Main to isolator to second. Neg from second to chassis and to main and isolator to chassis.

    I hope all that makes sense

    • Andy says:

      What I do is have a switch that is powered by the accessory battery to connect the relay when I want to manually connect both batteries when my engine is off.

  • Michael Strange says:

    Andy – what a terrific wright-up on the subject! Thank you! I have just one question for you… As you started this post in 2013, is there a different Dual Battery Isolator that you would install today? I plan on following the guidelines you have shown us here, to modify my 2012 Chevy Avalanche.

    • Andy says:

      I would do the wiring myself now. But I think I would stay with the 200-amp can relay, it works well after 9 years. Besides using the engine idle sensor fuse tap to activate the relay, I also have it connected to a voltage-activated relay on my solar panel, which closes the relay to starting battery when the solar panel is above 14.4 volts and disconnects the starting battery when the solar panel has less then 13.1 volts coming in so accessory loads don’t drain the starting battery.

  • Mike says:

    A very helpful thread. I have a 2018 Chevy Silverado and have seen articles that say I need a DC to DC charger vs an isolator per your solution. I was just about to install a 140amp Isolator and found articles about issues with the “smart” alternators making he isolators not work correctly. In my truck I usually have a cell phone charging and headlights on – so I consistently have 14volts or more being generated. So my question is – Isolator or DC to DC charger for the 2018 Silverado? Thanks!

    • Andy says:

      Attach the ground of your second accessory battery to the starting battery rather then the frame, to ensure the voltage regulator see the current flow on the neutral line, remains in charge mode until both batteries are charged. Then you can use an ordinary 200-amp can-style isolator switched via the engine idle sensor fuse being hot.

    • robert howard says:

      wondering what you decided on i have 2017 Silverado and do some back woods camping

  • Ryan Kennedy says:

    i was wondering about your isolator is it a “smart” isolator ? did some reading that some of the newer trucks require a smart isolator to not mess with any of the computer settings in the truck that communicate with the altenator. i had picked up a similar isolator to yours before reading into that i have 2011 sierra have you ran into any problems with that isolator if it isnt a smart isolator?

    • Andy says:

      The smart alternator works by monitoring the current on the negative wire on the battery. Connect the accessory battery neutral not to the frame but to the neutral of the starting battery to avoid confusing the alternator.

  • Ty says:

    Would this setup work if I wanted to jump my starter battery off the auxiliary battery or would I need to wire in a switch? Or do you have a suggestion for how to incorporate both this diagram and the ability to jumpstart?

    • Andy says:

      Just put a switch between the relay and the hot on the accessory battery.

    • Galileo says:

      As Andy mentioned, the solution here is to setup a switch for the relay. I decided that given I was doing the wiring myself, I wanted to limit the number of places where I could make mistakes and leave the heavy lifting to the electronics manufacturers.

      Found this: https://www.amazon.com/Isolator-Universal-Sensitive-Off-Roader-Protection/dp/B08BHWQKRP

      By the looks of it, someone has had success with the 150A model on a Silverado 1500 4.3L V6 (which is shipped with a 145A alternator, some of the other models ship with a 160A in which case you want the 200A isolator). It has the switch built into the unit, so you can press the button on the side to get pass-through for jumping the main battery.

  • Bill says:

    An excellent write up.
    I am adding a second battery as well as my Lance camper ( with house battery )to the mix.
    Im sticking with conventional marine type batteries for second batt and house batt at the moment as I have 2 good ones.
    Do you think I should or could wire the house battery directly to my aux battery with an inline fuse ?
    I think my 2020 Silverado 3500hd 4×4 WT has the “smart” alternator system.
    Thanks, Bill

  • Smitty27 says:

    Silly – several times you claim the “appliances” you need the 120v inverter for includes an “alarm clock.” Huh? Camping? Alarm clock? And you have a cell phone – what about just using your phone for that? A 120v alarm clock? Not a battery powered alarm clock? Or a windup alarm clock? Wow, definitely worth running all that so you can plug in a 120v “alarm clock.” Camp lighting should be a camp FIRE and maybe some low amp, low volt 12v little stuff. Same with your cell phone charging system you claim the inverter is needed for. *facepalm* Are you powering a giant disco ball above the tent and a long string of old blackberry phones? Too many of these articles just scream FAKE.

  • David Brown says:

    Andy πŸ™‚ I know it has been many years since you wrote this article so hopefully you are still replying to questions. I have a 2010 Silverado LT Z71 with a trailer package minus the brake controller installed. I do a lot of camping with family and I like your initial setup for the auxiliary battery but would do the work myself(to save money). Could i use a diode based isolator instead of a can type isolator. I read in your article that you can’t but there is a special one if i can go from the alternator to auxiliary battery instead of the starting battery that would be easier? What specific diode based isolator do they manufacture that i can do that or should i just stick to the regular can type isolator? Also the 2 lugs on the end of the fuse box next to the battery can they be used for any kind of power? I know they are used for the trailer brake controller and 12volt source to trailer. Thanks for the help

    • Andy says:

      The problem with a diode based isolator is you get a voltage drop (0.6 volts) which means you accessory battery won’t charge as well. Likewise, you will have issues with the voltage controller not sensing the low battery on the accessory side of things, so it won’t excite the voltage regulator sufficently, so the alternator voltage will drop when the starting battery is fully charged and the accessory battery isn’t.

  • Hutch says:

    I have a 2013 Silverado z71 with trailerpackage. It has charging system for trailer. There is a second battery tray in truck. There is fused line from starter battery over to main fuse block. Can’t find out if already set up for extra battery.

  • Dorn says:

    I have an 04 Yukon, and the factory battery is on the driver’s side. I want to add the second battery to the pass side, but all the info I find they are using the same battery that would be factory and it is too tall to put that corner brace back on. What size is your factory battery? It looks to sit nicely under that brace.

  • Robert Newton says:

    I have a 2011 silverado with the dual battery set up, works fine. Both batteries are the same type, age. They are both AGM batteries connected as described above, with no isolator. I am wanting to add a third agm in the cab of the truck, but it will be on a isolator as it is older than the other 2. Do I need to connect the 2 batteries ground to the third? Or connect the third battery to just the frame? For the sensor to work correctly for the 3rd battery. Thanks.

  • Chris P says:

    Hi Andy,
    I am performing this modification to my 2013 4.8L Silverado LT and am doing nearly the identical setup but will mount a Blue Sea fuse block on top of the truck’s circuit block cover for accessories. You did a great job with your truck and your blog is a wonderful resource for those of us that don’t drive Tacomas. I read through all the Q & A several times and am left with only 2 questions:

    1. In July of 2013 the question was asked, which fuse number you tapped according to the circuit block diagram. I didn’t find an answer to that question. Based on the limited abbreviations on the block lid, and your photo being slightly out of focus, I want to be sure I’m pulling the correct fuse. Thinking it’s number 8?

    2. Will 16 gauge wire work for the fuse tap and small ground wire from the isolator?

    Thanks for posting this blog. Very much appreciated!

  • John says:

    Great write up, very clean install and photos. My only complaint is where you’re tapping. Never tap an essential engine part. Always use an ignition power source that’s non essential, like DRL, trailer power, acc socket, etc. those won’t affect the safe operation of the truck in case of a circuit failure of some kind.

  • Mark Bergren says:

    The information in this site is great!
    In researching the after market installation of second battery I came across the GM recommendation (Electrical Manual – 2011 Light Duty Full Size C/K Trucks Electrical Manual – 2011 Light Duty Full Size C/K Trucks, and GM service bulletin that can be found at https://static.nhtsa.gov/odi/tsbs/2015/MC-10113732-9999.pdf) to install a diode, P/N 12112422, across the coil of the solenoid of the battery isolator. I don’t see any mention of this step and I am wondering if it is needed. I am about to add a second battery to my 2011 Silverado and would appreciate thoughts.

    • Kevin says:

      I came across that TSB as well so I added a 400V 3A 1N5404 diode to mine just in case. I’m using the PAC200.

    • Kevin says:

      I saw that TSB. I used a 1N5404 3A 400V diode on my PAC200. No issues that I can tell. Verified that everything is working as expected using a multimeter and current sensor.

  • justin says:

    What fuse number do I tap into. I would appreciate it if someone could just mention a number instead of an abbreviation. Thank you!

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