Loose part inside pre build Battery pack

So i noticed something ratteling inside my Battery so i opened it up and found a small part that has de-soldered itself. I don’t know what it is and how important it is but I assume any use would be risky. If I am lucky it is from the built in USB port which means the battery is still good but I have no idea. The battery is a 10s4p from AlienPowerSystems, I have had it for a while without any issues apart from a bit of sagging. Any help would be appreciated!

Easy enough. The cap on your usb PCB is missing