How to calibrate if ifixit replacement battery

Any aftermarket battery should be assumed to not work with the iOS battery health check unless the seller guarantees it will work. Almost none of them will.

The problem is iOS only registers the OEM Apple battery properly. 3rd party batteries usually use a different vendor ID (which Apple uses to ID 3rd party batteries). This is done for legal reasons because of how ruthless Apple is to companies who cost them additional revenue/new device sales because they inflated the price on purpose to force a device upgrade.

As a result, Apple takes advantage of this (and uses it as a way to nudge users to pay them to do it) and checks for a vendor ID in the battery firmware. Spoofing the firmware gets around this problem, but it’s a legal nightmare for sellers and the factories producing the battery. No US company will dare sell those batteries without lying about it so Apple doesn’t have as much ground against them.

It’s safer to sell incompatible/no guarantee batteries then take the legal risk.