Isolator Or Not?

[Thurman]

I have an '07 GMC, CC, NBS, 5.3, Z71, 2-WD. I'm wanting to add a second battery to this truck and am getting conflicting stories as to adding a second battery to any GMT 900 series truck starting with the 2007 NBS series. One story is that you do add a battery isolator for the second battery, the other story is that the '07 NBS and later models have an internal isolator and basically all that is needed would be some cables, connectors, and a relay from a GM parts counter, #12135194. Both of these stories are coming from two different GMC dealers in separate towns. The local Chevy dealer's parts guys actually didn't know but looked up the relay and told me that it was for an '07 NBS--'09 GMT 900 series for use with second battery install. The dealer who told me that the relay and some over-the-counter cables would be all I need says I basically have the "snow plow package" which is the option the second battery would be included in from the factory. Can anyone straighten me out, on this item? Thanks, David

[kundog]

First off, I don't know why a isolator would be required...you want two batteries for more starting amps or severe duty cycles due to a plow pump? I have two batteries connected in parallel, and have no such issues, no idea why all this added "stuff" would be required and sounds like non-sense to me, but then again I have seen some strange and interesting things.

[grose67]

Do a search on adding a second battery. A while back there was a pretty good discussion with instructions. Here is one. http://www.gm-trucks.com/forums/index.php?...=second+battery

[Thurman]

The second battery issue has nothing to do with a snow plow application, I believe the last time it snowed here was in '72. The issue is that I have had the battery replaced twice in this '07 Sierra under warranty. The selling dealer states that it should have had the second battery from the factory as it has the Z71 package, but is 2-WD. The area service rep got involved and agreed that there is a code in the glovebox which states my truck should have gotten the second battery, I have no idea why. But--they will not install it under warranty. The selling dealer and the factory service rep told me that all '07 NBS and later GMT 900's have the built-in isolator and only need the battery cables, the relay, and a few small items. As stated if you can come up with battery cables at your local parts counter then you only need the GM relay. And I'll make this statement: I'm dealing with mediocre local GM parts guys also, so information is not too accurate. Thanks, David