GM DUAL BATTERY CONVERSION

Upgrading to dual batteries gives working Chevy/GMC 1500s a big electrical buffer

by Bruce W. Smith

Inverters, coolers, radios, warning strobes, laptops, battery chargers, printers and other necessary accessories put a big drain on any pickup’s stock electrical system when the truck is sitting on a jobsite with the engine off.

Even with the engine running the amp load needed to power such an array of accessories can put a strain on the stock electrical system.

Add a plow, connect to a weak trailer battery or flip on auxiliary driving, fog or work lights and the battery is going to take a hard hit.

In preparation for adding an inverter, warning lights and a few other work truck “necessaries” on Project Bedrock — our 2011 GMC Sierra 1500 Crew Cab 4×4 – we decided it was a good idea to double-up the batteries.

Stock Chevy/GMC 1500s come with a single Group 48 battery located in the passenger’s-side rear corner of the engine bay.

There’s also an unused battery tray on the driver’s front corner; there’s no TP2 (dual-battery option) for the 1500s, so it’s a mystery why it’s there.

Wiring diagram that comes with the Cole Heresee 48530 Smart battery Isolator lines out the installation.

Whatever the reason, it does make it easy to double-up the batteries. All you need is a GM Battery Retainer (#14005061) that costs less than $5, a second battery and a battery isolator designed to work with the new electronics.

THE SETUP

The factory AC-Delco Group 48 battery is unique to GM trucks, and it’s rated at 615 CCA (Cold Cranking Amps) with 110 RC (Reserve Capacity).

It’s almost identical to a Group 34/78 or Group 78 battery. So we chose an Odyssey 78-PC1500-A AGM battery as the auxiliary, which delivers 880 CCA and 135 minutes RC.

The Odyssey is far more receptive to deep discharging and resistant to the hard pounding from off-pavement use than the OEM battery.

We converted our 2011 GMC Sierra 1500 to dual batteries using an Odyssey 78-PC1500-A AGM battery and Cole Hersee Smart Battery Isolator. C/H Low Voltage Disconnect was also installed.

To connect the two batteries properly, we selected a Cole Hersee Smart Battery Isolator (#48530) designed to work with today’s electronic charging systems.

The 200-amp isolator senses the voltage of both main and auxiliary batteries and connects/separates them according to their charge, always protecting the main “cranking” battery.

SMART ISOLATOR

For example, you pull the truck in to a jobsite, turn the engine off and leave all the warning lights on.

When the isolator senses the batteries reach 12.7V it opens the solenoid relay to separate the two batteries and turns off the status light.