I'm using Yamaha THR5 electric guitar amplifier. It's possible to power it with batteries. It isn't economically good solution though. Something rechargable would be way better. Since I had a Li-Po battery lying around I made a small dongle which regulates the voltage.
The dongle in a 3D printed casing. Two switches allow breaking input and output circuit independently.
Step-up converter is based on LTC1871 chip. The PCB has built-in radiator and a display which shows output/input voltage (toggleable with a button). Easy to setup output voltage and monitor the state of the battery. Sweet!
Ugly cables bother me so I usually wrap them in nylon tubing. It's a cheap way to make them look better. Short heat-shrink tubing holds the ending of the tubing.