The chassis AGM, is it not an ACdelco AGM?
These have been coming up on Amazon searches in most car jar group sizes, with free shipping and a good price, for an AGM, and people see the AGM and seem to think it is then a super magical, physics defying battery, and the extra price over a flooded jar then confirms it in their minds.
2 of my neighbors are asking me about these AGMs, and I say i'll let them know what I think of this brand if they get them, but if they are Johnson Controls made, I would no bother with one over a flooded starting battery, as all of them seem to believe leaving the doors open overnight with dome light on is of no consequence as the alternator instantly and magically recharges it to full in that mile drive to the store and back, and it is 'still going strong' despite falling to 8.1 volts when turning their starter motors at 70F ambient.
The CCA's of these budget friendly AGM are hardly if any any better than their lighterweight flooded counterparts. The main benefit would seem to be lack of, or reduced terminal corrosion, if the owner installer actually cleans off the existing post clamps before installing them on their new 'super AGM' battery which is somehow perceived to be magically immune to abuse because of those 3 letters and the extra price paid.
Battery Marketers are well aware of this cash cow. I wonder how many corners can be cut on manufacturing of an AGM. I'd expect them cut diagonally, on batteries marketed towards starter battery duty and sold with free shipping.
When I saw the heat report on that first battery I thought about the connections, and any corrosion cleaned of with sandpaper still screams resistance, heating and invalid test results regarding the heating, and the voltage held during load.
Regarding resting voltage, One needs a basis for comparison. All these Fiamm's seem to get charged for different amounts of time and various degrees of 92+ %, rendering the full charge resting voltage meaningless, as they are not fully charged, except for the one that was held overnight at 14.4v.
And 14.4v overnight once is not going to heat it or damage it. My AGM has been held at 14.4 to 14.7 12 hours after the amp threshhold indicating full charge, has been breached dozens of times. Amps just keep tapering and my battery termperature is barely elevated at all. When newer, amps would taper to 0.0x amps at 14.7v given enough time, the X as my ammeter's cannot accurately measure hundredths of an amp less than 5. Now at ~800 deep cycles and many years of use this tapering stops in the 0.1 to 0.2 and perhaps 0.3 range, but a significant depletion event followed promptly by 65 amps applied until 14.7v, then holding it for extended periods will have it taper to 0.1 again and performance seemingly restored.
The 12+ hours of 14.4v likely will have that specific battery outperform the other batteries if all the variables are removed from the testing from battery to battery.
As for 12.85v on that ACdelco AGM, that could be perfectly normal for that specific starting battery.
It might also want 50% discharge cycle and 25+ amps applied until 14.4v is reached, then held until amps taper to 0.5% of capacity, before it will hold any higher resting voltage. My Northstar AGM refused to hold above 12.9v no matter how long I top charged it when new.
It took one deep cycle and 25+ amps recharge rate before it would hold its 13.06v resting voltage. It also cranked the engine noticeably faster after that first deep cycle and high amp recharge, and it still does this today 4.5 years later. Low and slow recharges after deep or semi deep cycles, piss it off and performance declines with each one, but a 50% depletion with 40+ amps until that ampthreshold is reached has it happy and holding impressive voltages under load thereafter for several cycles.
So I would not consider what you did as a valid test, I would see it as collecting some data for future comparison with a large number of asterix's next to those results.
HOld each battery at absorption voltage until they decline to a certain level, then let them rest for the same period of time, idealy at the same temperatures for no load voltage testing, and then perform your load test, and whatever method you are using to hook load to battery needs to have minimal resistance and be the same for each battery.
Alligator clamps with corroded clamps with corrosion 'sandpapered off' cannot and will not yield a good electrical connection. They will not even yield a comparable connection from battery to battery, rendering results invalid.
Alligator clamps are designed to dig into the soft lead(PB) of the terminals and the post clamps of batteries. If they are not digging into them, there is Very little surface area contact between the two.
AND most alligator clamps are just steel. Hardly a great conductor to begin with.
If one is going to perform tests for comparision, one needs to eliminate as many variables as possible, and have the same starting and end points. No, this is not always possible or worth the effort. Tests without accounting for the variables in comparison, would merely point out a used battery not worthy of employing, if excessive resistance at the battery terminal itself from a crappy electrical connection, is not the reason for the perceived poor performance.
So I'd gt a new way to connect load to battery, and fully charge each battery until the amp threhold is reached for the resting voltage a day later, and then load test it with those good electrical connections.
Results of those tests I would put some weight into, but testng batteries not known to be fully charged, and with variable quality of electrical connection, is not worth the effort of testing, in my opinion.
