You can reset the speaker on the JBL by holding down the Bluetooth and volume down buttons for 5 seconds. This works on the JBL Go and JBL Flip. To reset The JBL charge, hold the play pause and volume up buttons until you see the power button glowing.
If this hasn’t resolved your issue, there might be a hardware issue with the speaker itself. Possible problems are as follows:
* Charging port
* Charging circuit
* Battery
If your speaker is 5+ years old, then there is a good chance it has had more charge cycles than what it was rated for.