I'm surprised no one has mentioned this yet *edit* (oh someone did but didn't include a link) Amazon.com: Baseus Power Bank, 65W 20000mAh Laptop Portable Charger, Fast Charging USB C 4-Port PD3.0 Battery Pack for MacBook Dell XPS IPad iPhone 14/13/12 Pro Mini Samsung Switch : Cell Phones & Accessories
and some velcro to slap on the power to the bank of my syntakt has been working really well. I get a few hours of play time per charge.