Portable power for Yamaha Amplifier

I’m using Yamaha THR5 electric guitar amplifier. It has an option to power it with batteries. Powering it with batteries seems not efficient though. It would be way better to have something rechargable like Li-Po battery. In this project I made a small dongle which allowed me to do just that.

A way to power the Yamaha THR5 amplifier with Li-Po battery.