I would be very careful trying to use that battery again.
https://youtu.be/-ZLB2RB3bWIOf course it could be just a faulty connector, either on the battery or on the battery holder side. Try to search "Hailong Battery Case Power Discharge connector Plug 4pins 5pins Male" or with similar words, Rad's battery case looks pretty much same than the HaiLong made.
And you should check for shortcuts on the battery holder connector, and also check the voltage of the battery.
Of course these are just and only my best guesses without any real knowledge about repairing any kind of faulty ebike batteries!