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Title:Installing a second battery

Author:Doug of the North

Well, if you do a lot of off-roading, or have a lot of accessories, you may want to consider dual batteries. In the winter, they can give you that extra bit of starting power.

There is a downside to this however; it will place a bigger demand on your charging system. An upgraded alternator is recommended.

There are three basic setups for dual battery systems.

1. Simple: 2 batteries are connected in parallel (+ to + and - to -). This is the easiest, but if both batteries are not EXACTLY the same, it will eat batteries.
2. Solenoid isolated: This setup is basically the same as the simple, but with a giant relay that only connects the 2 batteries when the engine is running. This is better, but problems with excessive voltage spikes occurring when the solenoid closes can wreak havoc with electronics (aka PCM)
3. Diode isolated: This setup ALWAYS has the 2 batteries on separate circuits. This is the best setup, but you will need a more powerful alternator, the diodes eat up some of the current.

What you will need:

• Diode isolator rated to at least 140 amps for GM
• alternators (get a bigger one to aid cooling).
• 4 gauge or bigger wire (from where you want the 2nd battery to under hood)
• Battery box
• Battery
• Battery posts
• Ring terminators for the 4gauge
• 8 gauge wire & terminators from alternator to isolator
• 12 gauge wire

Install battery box (bolt to ground) and run a vent line (hose) to the outside of the cab. Install battery, and run a 4-gauge line from negative post to the floor pan (MAKE SURE to clean the metal to get a good connection).

Run 4-gauge from second battery to engine compartment. USE GROMETS WHEN PASSING THROUGH SHEET METAL!

Mount isolator into engine compartment. Run wire from the small post on the isolator to an ignition switched lead. This will provide the alternator sense when the engine is running.

Now, at the main battery, there is a large wire and a small one in the + connector. Cut the small one about 6 inches from the battery.

At the alternator, remove the nut and the 2 wires. Figure out which one goes to the battery (it is the same wire that was cut before), and completely remove it. The other wire will need to be extended with 12-gauge wire, and run to the Battery 1 post of the isolator.

Run the 8-gauge wire from the output post of the alternator to the ALT post on the isolator. Now connect the 2nd battery + line to the Battery 2 side of the alternator.

Reconnect all battery connectors, and start engine (MAKE SURE ALL WIRES ARE CLEAR OF MOVING PARTS ON ENGINE FIRST). It should show a normal charge rate. Now take a voltmeter, and check the voltage of both batteries. They should be very close.

Now, secure all wires.

Congrats, you have a full dual battery setup.

One other thing you can do, is get a 200 amp starter solenoid, and run 4-gauge between battery one, and the input terminal of the solenoid. Then run 4-gauge from battery 2 to the other main terminal of the solenoid. Now, run a small ground to one of the control inputs, and power, through a momentary switch in the cab, to the other input.

This way, if, in the winter, you need extra starting power, you can push the button and get twice the starting current.

Ircmaxell
Edited by Dougofthenorth
Rev. 2004 Aug 2