What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[gooffeyguy]

Sounds like it's not accepting a full charge since it comes up so quickly. Might try a desulfate cycle if your charger will do that.

I just went out and checked the voltage with a meter on the terminals and it's at 10.2v and will not start. I'm gonna pull it and charge it out of the vehicle and see if it loses charge while sitting on the bench

 

[Rocket Man]

Good process of narrowing down any parasitic drains from the stuff you've added.

I've had some mixed results with AGM batteries behaving in exactly the same way in older vehicles. Most recently in our '05 Infiniti G35X. It acted EXACTLY like there was a parasitic drain, and the AGM battery was maybe 18 months old, IIRC. It would go dead within 48 hours and I spent a ton of time trying to find parasitic drains. Swapped it with the cheapest Autozone conventional battery I could find, and now it often sits for 2-3 weeks without being driven, no problem at all.

One theory I have is that the factory alternators on our trucks (and most pre-2015 cars) don't charge AGM batteries in the way that they need to be charged for longevity. It's purely a theory, but when I replaced the alternators in both of mine with new Chinese units and new AGM batteries, I haven't had a problem since and it's been 4 years on one of them now. Prior to that they both ate new, expensive, German AGM batteries within a year.

I’ve had Interstate AGM ‘s in both my trucks. The 02 has been 3 years iirc and the 08 has been 2. No issues so far.

 

[denalilex]

spark plugs, u joints, stared at it on the jack stands that it has all but welded it self to, & pulled & discovered that dreaded 1-2-3-4/3-5-R clutch housing….cracked

 

[swathdiver]

So I looked at the battery and the date code on it is 11/19 so it's only been just over 3 years. It has a 3 year warranty (Everstart Maxx from Walmart).

When I first hooked the charger/conditioner to it, it said the voltage was 11.1v. I started the charge cycle and the percentage started at 0% and was at 1% in a few minutes. I stepped away for about 15 mins and when I got back it was at 100% and in maintain mode.

It started fine and while idling with the Tech2 hooked up it showed ignition voltage at 14.28 or 14.58, I can't remember. So the charge circuit seems fine. I need to go check the standing voltage now that it's been sitting for about 2 hours

Tom, use the Tech-2 to see what the start up state of charge is and the state of charge after sitting overnight. If it is less than 64% GM says to replace it. A tender may resuscitate it but only for so long at that age.

Go into the BCM, then BCM again and Charging Info section to see the values. Also, if the battery is hot, that's a sign she's not taking a charge well too and is wore out or needs reconditioning. My menus may be a little different from yours but this stuff resides in the BCM and not ECM.

 

[gooffeyguy]

Tom, use the Tech-2 to see what the start up state of charge is and the state of charge after sitting overnight. If it is less than 64% GM says to replace it. A tender may resuscitate it but only for so long at that age.

Go into the BCM, then BCM again and Charging Info section to see the values. Also, if the battery is hot, that's a sign she's not taking a charge well too and is wore out or needs reconditioning. My menus may be a little different from yours but this stuff resides in the BCM and not ECM.

I'll try that tomorrow.

With it sitting on the bench and charging with that new Schumacher charger I got, it will charge up to 60% then say charge complete and go into standby/maintain mode. Disconnecting the charger and testing with DVM it's at 12.6v, a half hour later it's at 12.4v. I'll check it again in about an hour.

 

[swathdiver]

I'll try that tomorrow.

With it sitting on the bench and charging with that new Schumacher charger I got, it will charge up to 60% then say charge complete and go into standby/maintain mode. Disconnecting the charger and testing with DVM it's at 12.6v, a half hour later it's at 12.4v. I'll check it again in about an hour.

12.4 V is in the 60% range and probably means she's about had it Tom.

The charger is stopping because of resistance encountered or calculated heat.

 

[gooffeyguy]

12.4 V is in the 60% range and probably means she's about had it Tom.

The charger is stopping because of resistance encountered or calculated heat.

I just went out and checked it with a meter and it's down to 11.8v from the 12.6v it had. This is just sitting on the bench in the garage for the last 3 hrs after being charged with nothing plugged into it.

Think I'll be running to Costco or Walmart tomorrow and getting a new one. Might get the AGM

 

[swathdiver]

I just went out and checked it with a meter and it's down to 11.8v from the 12.6v it had. This is just sitting on the bench in the garage for the last 3 hrs after being charged with nothing plugged into it.

Think I'll be running to Costco or Walmart tomorrow and getting a new one. Might get the AGM

You'll see no benefit from an AGM with our charging system. Check out the 48GHR or 88866212. I put one in the Sierra last year and it's the replacement for my 48HPG which is 29 months old now.

I'd say that thing is toast too.

 

[Doubeleive]

My interstate agm's are approaching 3 years this summer, no issue's so far but I haven't had battery make it 4 years ever in CA. the heat does them in. atleast costco has them reasonable when the time comes again.

 

[gooffeyguy]

The AGMs have a 4 year replacement warranty while the standard has a 3 year.

Costco sells Interstate brand. Standard is $119 while AGM is $169

Walmart has the Everstart brand, priced at $159 standard and $179 AGM (I get 10% off these prices at Walmart)