That's the port to the battery data cable connecting to the battery board. Unfortunately, the battery board is permanently connected to the battery. So, if you aren't able to solder the port back onto the battery board, you'll need to replace the whole battery. There may be an easier way to repair the connections between the battery board and the port that broke off, but I can't recommend any to a DIYer.
[product|IF123-156|Here's the replacement battery|new_window=true], which shows the battery board with the port (for reference).