He already has the battery which, as I understand it, he received virtually for free. I see no reason not to use it at some point.

 

Exactly, and AGM batteries need to be treated differently than flooded.

The OEM battery is not an AGM, it is flooded. The AC Delco direct replacement is also flooded. It is pure speculation the system is designed to also accommodate AGM batteries. As you point out "we will will never know the algorithms that are used."

If you come across anything from GM stating AGM batteries are appropriate for the Corvette, pass it along.

 

Solid technical fact based input...not.

 

I agree with your premise, that he already has the battery which was free, but not your conclusion. Given what I know of Optima batteries, I'd sell it and put the money toward a better battery (or something else I want for the car).

 

The AGM battery will not harm the electrical system in any way. Putting AGM batteries in boats with older charging system almost guarantees that the batteries simply won't last as long. That's the whole issue. Now if you need the high power use while not running the alternator, then AGM should be considered. The trade off is lower battery life.

Must assume that the GM charging system is the same as it has been for decades. A simple ferroresonent system that does not control the charging rates. As the battery charges, the battery voltage comes up. The alternator output stays the same therefore difference between battery voltage and alternator output voltage gets smaller. As the difference gets smaller the charging rate drops (less amps into the battery), until the battery is full. Thereafter there is a small charge going into the battery because the battery can't get up to the alternator voltage in most cases. Simple as that. And this has worked for flooded wet cells for decades.

In the case of any AGM step charger, the initial charging voltage ramps up to maintain a constant charging current (bulk charge, 10s of amps depending on size of battery). When the voltage of the battery rises to a predetermined amount (typically in the high 14v range) the charging current is reduced as this voltage is maintained (absorption charge). Then the charging voltage drops to somewhere in the mid 13v range when the battery will absorb no more current. It then enters the float phase. Graph attached. Apologize if TMI for some....

Point is that this is what it takes to properly maintain any AGM battery (yellow top, pink bottom, black square etc). Not doing this shortens battery life but won't hurt anything. This was painfully learned in the marine industry as the new AGM batteries came out but the charging systems were old style designed for flooded wet cells. Today's marine chargers all have selections for different battery types or they just do let's say AGM and Gel cells. Flooded wet cells work perfectly fine with the Step Charging required by AGMs and Gel Cell batteries.

To summarize. Your buddy may swear by them. His cousin may have had to replace the yellow top many times, etc etc etc. Depends on use and how they are maintained. Those little maintainer chargers don't come near the charging rates needed to keep an AGM healthy if hooked up in discharged states (other than slight). Only a proper step charger should be used. If you have a maintainer that does step charging, great, use it. If you have an AGM battery make sure it does step charging. Worst case is if you go somewhere, then drain the battery using loads with the engine off, then have to depend on the alternator to recharge it while going home. But if you need this moderate discharge over longer period of time an AGM (a type of deep cycle battery) is probably for you. The only thing you will affect is the cash in your pocket in the long run.

Oh, and calling Optima may be like calling the Chevy dealer and asking if you should order a C8 :-)..

 

Do I understand you correctly. Are you implying that all commercially sold consumer portable automotive, AGM capable, charger/maintainers are incapable of properly charging and maintaining an AGM battery? I understand the charging cycle of a AGM battery and what its' strength are. If this is what you are claiming then you may be the only person that has made this claim. Manufacturers of these chargers would disagree with your suggestion if this is what you claim. You realize many Corvette owners use these batteries and you would be hard pressed to find owners that are not pleased with their performance.

 

Another one of you insubstantial posts on the forum? You're getting good at this.

 

Somewhere I thought I had read that Optimas had a tough time fitting in the C7 battery compartment.....

 

Nope. Just saying that the car’s alternator is not a suitable agm charger. They would never go through the expense of a step charger and throw a flooded wet cell. Many EXTERNAL chargers are made to handle step charging. Where is the bulk of your charging done? Hint: not by the little maintainer in the cigarette lighter. Compare the cable size on a real external charger to the little plug in maintainer.

 

The little plug you refer to is on a 20 amp circuit. I own a 7 amp charger and I also have access to a 15 amp charger. I trust these companies that manufacture these devices when the say their chargers are capable of charging 12V AGM car batteries. So do you believe they are deceptive when they are making these claims? What are you calling a "real" external charger?...50 amps? CTEK believes 4.3 amps is sufficient current to charge a 12V AGM. Also, numerous owners here are reporting at least 3 year life expectancy with this battery.

Do you have access to a notional charge diagram for a typical 12V AGM battery that has been deeply discharged? I'd like to explore this topic further.

 

Based on the statements made by some of the posters, "Don't buy it" or words to that effect, it seemed that they were unaware that he already had the battery in his possession for essentially zero cost. I was just trying to clear up that misconception. I couild see where the Corvette charging system may not be optimized for an AGM battery, thus shortening its life. I don't know whether that is the case or not. Perhaps he could sell it for enough money to buy an OE style battery. Or he could use it and perhaps not get optimal life out it. His choice. I don't know that I've seen enough data here to indicate that this battery will cause any problems in his car or damage it in any way.

 

There really is no special "optimization" required of the charging system within your vehicle other than there be no prolonged periods of charging above "about" 14 Volts (14.2V is OK for short periods) with an AGM battery installed. That's all. This claim is just another myth you will find from some on the forum. Very seldom will you see this occur on our C7s. AGM and flooded lead filled batteries are interchangeable with our vehicles.

 

Yes they are interchangeable but the charging system is NOT setup for them. Step chargers set for AGM will go into the high 14v range to get that charging current up. My only point is that the life of an AGM battery is reduced without dedicated step charging. Look it up at some battery manufacturer websites. I have no dog in this discussion other than to explain the technical aspects of battery charging. Marine techs are taught to never install AGM batteries unless the boat’s charging system is set up for it (shore power charger particularly since this is the charging source 98% of the time). Never said you can’t do it, just that it will likely reduce battery life. Over and out....

 

A tidbit of additional objective information:

"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25/cell (13.5V) and 2.30V/cell (13.8V) (summer temperatures may require lower voltages).

"Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive. Overcharging AGM batteries kills them. See, e.g, click and click.

As @Submerge noted earlier, this will not hurt the car but decreases AGM battery life.

 

"likely reduce AGM battery life" and "could overcharge" are such vague expressions as to have no meaning. Charging specs cited are all within Corvette charging system performance parameters and well within charging modes found in CTEK's charger/maintainers. Fear mongering this topic does not make your fears true. Plain fact is many people use these batteries in their C7s (and other vehicles as well) and have reported no issues with them. Charger manufacturers are well versed on the performance and requirements of AGM batteries as they have been around for many years. They stand by their claims their chargers are safe to use and compatible and with AGM automotive batteries.

 

As you admit, Then there is what we do know: The C7's OEM battery is flooded. The replacement OEM is flooded. Unlike BMW, the Corvette does not include the ability to tell the car what type of battery has been installed. We have no information the system self-configures to AGM. Overcharging AGM batteries kills them.

Those contemplating going non-OEM and installing an AGM battery should take into account the downsides of doing so.

Whether the individual owner considers the consequences is entirely up to them.

 

There are no indications the charging process that occurs in C7 Corvette is harmful in any way to the life of an installed AGM battery. Many Corvette owners are using this battery in their vehicles and we are not hearing any reports of issues from these owners. The CTEK uses the exact charge cycle to charge an AGM battery as it does for a flooded lead filled battery with the exception of it will charge the AGM at 14.7 volts (4.3 amps) during the bulk charge phase vice 14.3 V for the lead-filled. Maybe you should call CTEK engineers and tell them their chargers are not charging AGM batteries properly.
...

 

So much science! Well, my Optima Yellow Top is highly recommended if you have upgraded stereo and track your car. Get a decent AGM microprocessor controlled charger (CTEK, NOCO, etc...) and call it a day. My OEM died without warning (3yrs). That's the second GM OEM (ACDelco?) that left me stranded. Never again.

 

The CTEK also treats AGM differently in the Absorption and Pulse phases. That is, three out of eight CTEK phases differ between AGM and flooded.

But what a CTEK does is meaningless; a C7 does not include a built in CTEK charger as part of its electrical system.

In fact, as you pointed out previously, "We will will never know the algorithms that are used to control and direct Corvette's battery control module." Thus, evidence a CTEK treats AGM differently does not mean a C7 does. It is however evidence that AGM and flooded batteries need to be treated differently.

If you come across anything from GM stating AGM batteries are appropriate for the Corvette, pass it along.

Of course, it is your car. The battery police are unlikely to learn you used a different battery type than OEM in your car.

 

If you come across anything from Optima Batteries stating AGM batteries are inappropriate for <insert vehicle here>, pass it along.