If the the battery rattles inside the springs might have compressed and lost contact with the battery. Pulling the springs would solve this. Otherwise its actually fairly easy to open the front side. Review: Nitecore HC60
Just take out the four screws and remove cover. Hopefully, its just the wires diaconnected then its an easy fix. The USB charging board on the battery + side can also be taken out after you’ve desoldered the wires, you can check that too.
I had a HC70 that I sent back to nitecore because the battery pack stopped working and they did replace it. It took a few months before I got it back though.