JBL Charge 2+

Complaint:
after switched off, it take time to power on normally. when charger connected it turns on and works normal . (charger connect only for boot time. then all normal without charger). no hardware issue. switch ,battery all replaced for test. next only software chance.

want to upgrade firmware. but it not shows in JBL Portable app . any other way for updating this JBL Charge 2+ device.?