The older Revmaster engines used flooded lead acid batteries. A new class of battery is the AGM (Absorbed Glass Matt), RG (Recumbant Gas) or SVRLA (Sealed Valve Regulated Lead Acid). While there are likely differences between manufacturers, and often the same technology is referred to differently between these manufacturers, in general, the three types are the same. Much of the industry has reverted to calling them AGM. The alternator issue was being reported and associated from planes with this new battery technology installed. One might correlate the battery type with the stator degradation. Lead acid batteries have an internal resistance of around 11 milli ohms (0.011 ohms). The new AGM batteries have a lower internal resistance of of about 1/4 this or 3 milli ohms (0.003 ohms). Personally, we don’t believe there is any evidence presented that supports the argument that the AGM alone is at fault.
The low internal resistance is one reason the AGM batteries have such good CCA (Cold Cranking Amps) characteristic. In his book, Bob Nuckolls (The AeroElectric Connection) does a fabulous job of explaining the physics behind starting current and how the small change of reduction of internal resistance can have such a big impact on a batteries CCA. Bob has a web site and much of the text in the book is available online but the book is a great reference and learning tool, even for someone well versed in electronics.
There is another characteristic that the AGMs are known for and that is rapid charging. The web site, “Battery University”
https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm
claims a reduced charge of “up to five times faster.” This might imply (and many folks seem to conclude) that this means 5 times the current. While the peak current could (and likely is) higher than a flooded cell design, it is unclear what the true difference in charge current from an alternator is. I have recorded the standard current of a flooded cell and an AGM, when being recharged from a PMA supply. The typical difference is measurable but not 5x. I’ll post the difference in charge current but as an order of magnitude it is about 15% greater for an AGM.