Whats the story with AGM batteries and the GMT900?

[i6pwr]

I've read mixed opinions, some point to the fact the full size platform should maybe not use AGM batteries?

I need a battery, group 48 H6M, and would like clarification.

I'm fine with an Everstart MAXX flooded or Duracell from Batteries Plus.

Would prefer the AGM but not a deal breaker.

 

[D60]

Good question. I sorta pondered this this summer for an '08 LMM but wound up putting standard lead acids in it. Now this winter it seems to be emptying batts while sitting but THAT is not conclusive enough to prove anything.

I haven't had time to test for a parasitic draw and the vehicle is driven by multiple volunteers, all of whom are perfectly likely to leave a dome light on.

 

[eljefino]

I've fitted a voltmeter to my 08 Silverado.

It often runs at 14.7 at 35'F ambient, and I've seen it as high as 15.3. I think it monitors how low the voltage goes when cranking and uses that as a battery health indicator. The computer then over-charges to try to compensate.

Not an AGM expert, but I don't think they like it that high. Anyway, I present my data for your consideration.

 

[tyman]

I put a Duracell agm into mine and the only issue I had was when it was -10* out one morning in winter. Used a jump starter and it fired right up and never had that issue again. It only had 2 years on it when I traded the truck in but it worked very well for my 2011 1500.

 

[LenZee]

I've fitted a voltmeter to my 08 Silverado.

It often runs at 14.7 at 35'F ambient, and I've seen it as high as 15.3. I think it monitors how low the voltage goes when cranking and uses that as a battery health indicator. The computer then over-charges to try to compensate.

Not an AGM expert, but I don't think they like it that high. Anyway, I present my data for your consideration.

AGM likes a higher voltage than flooded battery. 15.3v is a little more than they require though.

 

[D60]

I've fitted a voltmeter to my 08 Silverado.

It often runs at 14.7 at 35'F ambient, and I've seen it as high as 15.3. I think it monitors how low the voltage goes when cranking and uses that as a battery health indicator. The computer then over-charges to try to compensate.

Not an AGM expert, but I don't think they like it that high. Anyway, I present my data for your consideration.

I can't speak to any of that but the diesels at least don't even start charging until it's been running for....a few minutes.....maybe more? Never tried to find the reasoning but it strikes me as kinda odd.

 

[meep]

I’ll favor the batteries plus Duracell variant on it being an East Penn offering alone.

I’ve run AGM batteries in vehicles which started with flooded, with no ill effects. 14.8V is acceptable charging voltage for AGMs in cyclical use… and the ECU will taper the voltage down as well. 14.4 is a nice float voltage for AGMs. Each of them may vary a little based on mfr recommendations, as well as temperature. the only drawback with AGMs in a lower voltage flooded application is they will need more time to charge, so short tripping could be harder on them. Neither of my vehicles maintains 14.4V - and the f150 is programmed for them. It cruises around at 12.4 and reaches 14.7 whenever decelerating.

 

[Chris142]

I can't speak to any of that but the diesels at least don't even start charging until it's been running for....a few minutes.....maybe more? Never tried to find the reasoning but it strikes me as kinda odd.

That's true with a lot of cars. I don't think it's minutes but it may be 1 or 2

 

[Jetronic]

I've fitted a voltmeter to my 08 Silverado.

It often runs at 14.7 at 35'F ambient, and I've seen it as high as 15.3. I think it monitors how low the voltage goes when cranking and uses that as a battery health indicator. The computer then over-charges to try to compensate.

Not an AGM expert, but I don't think they like it that high. Anyway, I present my data for your consideration.

But the AGM wouldn't drop as low during crankjing, so wouldn't be subject to overvpltage?

 

[Lubener]

I've read mixed opinions, some point to the fact the full size platform should maybe not use AGM batteries?

I need a battery, group 48 H6M, and would like clarification.

I'm fine with an Everstart MAXX flooded or Duracell from Batteries Plus.

Would prefer the AGM but not a deal breaker.

I wouldn't use an over priced AGM battery. Everstart Maxx would be my choice.

 

[Craig in Canada]

I've fitted a voltmeter to my 08 Silverado.

It often runs at 14.7 at 35'F ambient, and I've seen it as high as 15.3. I think it monitors how low the voltage goes when cranking and uses that as a battery health indicator. The computer then over-charges to try to compensate.

Not an AGM expert, but I don't think they like it that high. Anyway, I present my data for your consideration.

AGM likes a higher voltage than flooded battery. 15.3v is a little more than they require though.

Here's my understanding over the years:

AGMs like a higher "float" voltage but have a lower "maximum" voltage. To my knowledge, most AGMs have a hard maximum of 14.8VDC (I've read about some with 14.6). Above that, you're causing damage, even in the relatively short term. On the other hand, they like to float in the 14s to reach 100% charge and that would be a little high for a standard flooded battery and it would start "boiling off" water from the electrolyte mix. Normal float for a flooded battery is in the mid-high 13s.

If a vehicle cannot have it's charging system programmed for AGM (or designed originally for AGM) the benefits might not be there. On BMWs since the mid-2000s the car is coded for the capacity and type (AGM / flooded) of battery. The type-coding changes the charging profile to float higher but with a hard limit of 14.8VDC. In AGM mode, I have frequently seen EXACTLY 14.8VDC as the system voltage (until EfficientDynamics kicks in on the F- and G-series cars etc...etc...)

Personally (everyone can do what they like) I wouldn't bother fitting AGM to a car that doesn't know how to charge it properly. It might spend most of it's life not fully charged, and could be damaged by anything over 14.8.

 

[Snagglefoot]

We have an AGM battery in my son’s 2010 Silverado. After 3 years everything is fine.

 

[repairman54]

My '11 Tahoe OEM battery was an AGM. I put an Odessey in it in '18 not for issues but age and issues prevention. That AC battery has been on a Battery Minder since then and powers camper lights to this day.