What is the final word on if an AGM battery can be used in a 2021?

 

of course you can, an AGM be used anywhere that a lead acid battery can be used. There is nothing unique about them anymore. All the charging profiles are essentially the same.

 

I don't know if it is the final word but I used an H6 AGM battery in my C7 without problems. The C8 uses the same battery as the same as the C7. While the optimum charging profile for an AGM battery is slightly different from a flooded lead acid it doesn't seem to matter in real life.

 

I have not heard of any reason why an AGM battery could not be used in your C8.

 

Remember that AGM batteries want a different charger than the ones used on the old lead acid batteries.

 

ask yourself how a car can charge an AGM and a lead acid battery interchangeably. Camaro is use AGM’s standard now. They just aren’t that different anymore

and virtually all consumer charges now charge AGM and lead acid without any modification.

 

Bottom line up front: The charging system in the car is designed to maintain a Flooded Lead Acid (FLA) battery state of charge of 80% which corresponds to a battery open circuit voltage of 12.42. If the car charges the AGM to an open circuit voltage o 12.42, its resulting SOC will be 76%, which is a negligible difference. There is no indication in the Service Manual that it can detect the battery difference, but its possible - and if so - then it could do even better.

The C8 has a fairly sophisticated charging system. It has a battery monitor module. It will evaluate the state of charge of the battery by measuring the open circuit voltage (more or less) after the car has been sitting for several hours. When the car is running it measures charging voltage (system voltage) and also measures current going in and out of the battery (it sits between the battery negative terminal and negative battery cable). It has 5 charging modes depending on various factors. But the main mode is the fuel economy mode - basically the car targets a battery state of charge of 80%, which is an open circuit voltage of 12.42. That actual charging voltage for that charging mode is between 12.5v and 13.2v. This will presumably result in the targeted open circuit voltage (after the car has been off for 4 or more hours) of 12.42, which corresponds to the 80% SOC for the FLA.

So, the concern folks have is that the voltage vs state of charge is different for an AGM battery vs a Flooded Lead Acid (FLA) battery. Which leads to statements that they have a "different' charging profile. See attached charts.

The attached chart shows the difference. When fully charged a FLA open circuit voltage will be 12.6. But for an AGM it will be 13. A charger that is designed to take an AGM to 100% state of charge (SOC) might overcharge an FLA if the goal was 100% state of charge, and if the charger was only looking at voltage.

But, based on the description in the Service Manual, the goal of the C8 charging system is 80% state of charge. So for the FLA that corresponds to an open circuit voltage of 12.42. If the charging system in the car charged the AGM battery to an OC level of 12.42 volts, that would result in the AGM battery having a SOC of 76% instead of 80% (I did a linear interpolation of the chart values to get that). That is a negligible difference.

Its possible that the charging system goes further, and interprets the charging voltage vs current in real time - potentially making adjustments based on that - meaning it might be able to sense battery differences and adjust accordingly. But none of that appears in the description of the charging system in the Service Manual.

 

As sophisticated as the charging system is I wouldn't be surprised it the car can learn that an AGM battery has been installed. I.e., with 13.0v vs 12.6v at full charge the charge current fill fall off at a higher level.

 

So to what voltage will a Battery Tender tender charge an AGM?

 

I agree! It just not stated. But all the measurements are there - it can measure charging voltage, and it can measuring the resulting current in and out - presumable in while charging. So, it can build a profile of current vs voltage. If those are characteristic of the battery type, then it could distinguish them. It also knows the temperature.

As I have noted before, there is a field in the scan tool that indicates battery type - and options include Default, Flooded Battery, AGM Battery, Enhanced Flooded
Battery, or Lithium Battery. However, the expected value is "default", and there are no instructions anywhere in the manual about setting it differently for different batteries. There are, however, plenty of instructions for the setting of external test equipment to the proper battery type, but none regarding changing the setting in the car.

 

It depends on the maintainer, you'd have to check. But if the maintainer has desulfation capability you need to make sure it specifically endorses use on an AGM battery. You don't want to "desulfate" an AGM battery using the wrong cycle.

 

Honestly, I don't know. The chart shows the AGM is at 13 and the FLA is 12.6 for 100% SOC, Those voltages would be measured 4 hours after the charger is disconnected. The voltage may be higher while the charger is connected and also immediately after is it disconnected. You could measure the voltage while the charger is connected, but while it says the battery is fully charged, and see what it reads. I'm thinking its going to be on the order of 13.1 or less (I think that is the voltage for fully charged FLA immediately after it has been charged). But I am not sure. My battery tender has a switch to select between FLA/AGM (as one option) or LI as the other option. So it combines FLA and AGM under the same setting.

 

Completely 100% incorrect. you can use an AGM battery in place of a regular battery of the same group, and can use the same tenders.
AGM just means that the electrolyte(which is the same as a regular battery) is suspended in media (glass mat).
AGM stands for Absorbed Glass Mat, It can be a direct replacement with no special equipment or adjustment to charging systems or stand alone 12v battery chargers.

 

That sounds like an Optima battery. I used a red top in both my C5 and C6 with no problems. I went to the Optima because the AC Delco batteries split and spilled acid into the engine compartment. Never had any such problem with the Optimas.

 

In theory that's true, but many, many thousands of flooded lead acid batteries have been replace with AGM batteries without issue. I did that on my C7 and nothing went wrong with the car or battery in the 3 years I had the combo.

 

Copy that.
They're also better in cold weather, have a lower self discharge rate, can take a beating (last longer) in charge/discharge cycles, work upside down (although not recommended in your C8), and are maintenance free. They are usually pricier, though, but worth it.
As soon as the factory battery wears out in any vehicle I've owned since the early 2000s, I always replace it with an AGM. Drop in replacement. Done.

 

Personally, the Delco can give me 6-7 years and that's good enough for me. I've owned over 100 vehicles, 42 Corvettes and have never had any flooded lead acid battery cause any notable damage. That's even including the old Delco 'tar-top' batteries.

 

My 2001 Camaro's battery leaked after 34 months and damaged the paint under it, but I didn't notice until out of warranty.

 

My 911, as do all other P's, come with an AGM. Porsche "claims" that you must "program" a new battery and of course they want you to bring it in and get programed for the tune of about $190, even if you purchase a Porsche battery from them ($350). The claim is that a new battery charges differently by the puter system (but its not smart enough to detect a new battery). Many skip the tax and no one posts that their non programed battery takes a poop. When my OEM battery gave in I just replaced it with a Champion AGM - mind you, my Ctek has a AGM program that maintains it slightly different than a LA battery. Guess I'm a bad person.........

 

Audi says the same thing. Sounds like bs to me.