I had a phone with a faulty battery and it would simply turn off on a large current spike (think camera with flash taking a picture) presumably since the voltage crashed.
It sounds like the idea is that the OS is throttling the performance to extend the battery life of a battery in poor condition, more than it sounds like it is limiting current draw to avoid "brownouts".
I can see why this is a good idea and a bad idea, in that many people simply want a full day of being reachable on the phone more than they want smartphone features, but others who are considering replacement would like to know that a $100 fix would make their phone less frustrating.
iPad:~/ root# ioreg -l -w0 | grep Capacity | | | | | "Capacity" = 960 | | "BootCapacityEstimate" = 87 | | "BatteryData" = {"CycleCount"=232,"MaxCapacity"=10639,"FullAvailableCapacity"=11085,"StateOfCharge"=98, "MfgData"=<redacted cuz it looks like a unique id>, "DesignCapacity"=11560,"QmaxCell0"=11678,"Flags"=1,"ManufactureDate"="6205","ChemID"=4384,"BatterySerialNumber"="redacted","Voltage"=4155} | | "CurrentCapacity" = 10500 | | "BootBBCapacity" = 10364 | | "AppleRawCurrentCapacity" = 10242 | | "AbsoluteCapacity" = 11272 | | "AppleRawMaxCapacity" = 10489 | | "MaxCapacity" = 10500 | | "DesignCapacity" = 11560
I hypothesize that the MaxCapacity will drift lower over time. They have all the info they need in their registry.