Our battery cases can't fast charge the phone by themselves.
When saying fast charging, they allow more electricity to go through the charger cable to the phone.
Also, the charging speed greatly depends on the phone's input and output. Normally, we suggest our customer charge the phone with all the background programs off, which can reduce the battery drain and temperature loss, to accelerate the charging speed.
The important thing is that our battery cases can't be compatible with E-marker cables (those cables support a 60watts or higher charging speed).
A fast plug adapter is fine, but a super-fast cable is not.