I have had this system for a long time - using a PowerBank with the Wireless Adapter, Power On is easy as pie. The only way I've ever been able to turn off the Wireless Adapter/Headset is by disconnecting the power cable USB from the PowerBank. I've held the Power button for what seems long enough, but it never turns off.
If I don't disconnect the PowerBank, power is drained and it takes a long time to recharge it.