Does this exist? I would like to know if there is a portable battery that can power the x4, and where to buy it.
Portable power source for the X4
According to documentation, the X4 supports USB-C PD output up to 12V. So maybe a USB-C PD-compatible power bank with around 30W output? Just a random idea. Be careful while reading specifications because you need 30W on one output, but manufacturers like to add up the power available across all outputs.
In theory, any power bank that supports the 12V PD protocol can be used. I use this one and it works fine.