The volume is low when I use Mighty with a Bluetooth accessory.

If your Bluetooth accessory has onboard controls, press the volume up button until the volume is as loud as possible. Then, press the volume up button on Mighty until the volume is as loud as possible. You will then be listening at the maximum possible volume.

If you still feel that the volume is too low try disconnecting the devices, powering them both off and then back on, and then re-establishing the connection.