To achieve fast charging, you need to use an adapter with a power rating of 20W or higher that supports 9V2A (PD or QC). If you use a regular charger, you can only start normal charging, which reduces the charging efficiency by more than 30%. 

The battery level is calculated based on the real-time battery voltage, which is relatively accurate. However, errors may occur when the battery is installed in a camera. The reason for these errors is related to the camera mode settings and is a normal phenomenon. 

Due to differences in the actual battery capacity, there may be some error when inserting the battery into the charger. This includes the possibility of swapping batteries between the two battery compartments, which can result in an error of 1-2%, and this is normal. It is recommended to check the battery level while the battery is charging to avoid misidentifying a fully charged state due to a false charge. 

In charging mode, if the green charging indicator is constantly lit, it means that the battery is being charged in fast charging mode (9V2A); if the green charging indicator is flashing, it means that the non-fast charging mode (5V2A) is being used. 

Please check if the charging mode is green and the charging indicator is constantly lit, and check if the adapter has a 9V2A output; determine if fast charging mode is being used, as charging speed is significantly improved in fast charging mode.