Dual Battery Setup on My Silverado for Camp Power

Important Update: 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. 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.

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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.

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As long as you don’t drop the battery below 11.3 volts — 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.

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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 — occassionally being overly deep cycled — I might as well not spend a fortune.

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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.

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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.

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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.

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

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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.

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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. — Andy

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