There is a recommended service field manual from pylontech which says that all devices must (initial) charged to the 52.5 V with current ~ 0A before they should connected.
By the way maybe a well adjustable power sourch with normaly 0-60 V DC and 0-5 A is needed. I used the Cerbo to check for Cell Difference and Charging by using the DVCC Settings but can also use a normal switching power supply with 120 W output and 0-60 V 0-6 A PS.
There are a more detailed steps needed because the main goal is also that all parts are well balanced before connected. For US3000C here the steps which I read from the manual.
A) Charge with 48 V max with 2 A max. (new one)
B) Charge to 51 V max with 5 A max.
Now Balancing will start here:
C) Charge to 52,5 V max. with 5 A max. as long current will stop as before
D) Charge to 52,5 V max with 2 A max. as long …
C) Charge to 52,5 V max with 0,3 A max. as long cell voltage is less than 30 mV between all cells
The document itself maybe is confidential so I cannot share them, but you can simply ask pylontech for the information. I think they will give the information.