Why display going black

@adityavarma that will depend on how badly damaged your battery connector is. Most Likely, you will have to replace it. It is soldered onto the circuit board. You would need to desolder the old one and then re-solder a new one. Replacements are available. In order to do this type of soldering, you want to make sure that you have the proper tools and skills to do this. AS for your screen, does it show properly before it turns black or does it show anything at all on start up. I wonder how this is connected to the battery connector. Let us know how those parts got damaged. Use something like this video to work on your Oppo.