To be able to use the 4 port DJI Charger, you will need to activate it first, and here is how to activate your 4 port charger,
First download "DJI Assistant 2 for MG" by clicking the following link, and install it on your computer,
Then follow the instructions shown in the following video,
After you activate your charger successfully, the charger should start charging batteries without any issue. If you still have problem, please let us know with a comment. We will be happy to help you further more.