Analysis of the problem of iP8-iPXSMax not charging:

1. This issue mainly occurs under the following circumstances:

(1) The problem is primarily with iPhone 8, X, XR, XS, and iPhone XS Max models. 

These models have an overvoltage protection mechanism in the iOS system. If the voltage is detected to be 0.015V higher than the design voltage, charging to the phone battery will be disabled.

(2) It is concentrated in a specific dealer or customer. Specific dealers have a habit of pre-charging. Some customers have damaged or low-quality chargers with a significant difference in voltage.

2.There are three main reasons for the inability to charge:

(1) The battery has been overcharged:

Typically occurs when repair shops quickly charge the battery to 100% before installation to satisfy the customer. This is done using a repair DC power supply (rarely a direct charger for the battery), leading to excessively high battery voltage. 

Repair shops use externally purchased battery charging boards that are designed for universal new batteries at 4.45V voltage. Charging voltage is set relatively high, leading to overcharging for batteries before iPhone 11.

(2) Charger damage or poor quality:

Basic principle of transformers:

1) High-voltage AC is converted into qualified low-voltage DC for charging the phone, which is the charger's role.

2) The charger first converts high-voltage AC to low-voltage AC, then low-voltage AC to low-voltage large-ripple DC. This DC passes through a filtering circuit to become stable DC charging voltage that meets requirements.

If the charger's filtering circuit is damaged or of poor quality, it may exceed the standard voltage requirements, potentially causing overvoltage during charging.

(3) Poor data communication contacts:

Data communication is the primary task of the charging circuit to assess battery condition. Poor communication leads to unstable data and inability to charge.

Poor communication not only results in inability to charge but also issues like 1% battery jumps, inability to see health status, automatic restarts, etc.

Poor communication is often related to the phone's battery socket and battery FPC connector.