We need a powerbank with a built-in Bluetooth to 3.5 mm audio interface. People tend to carry a powerbank around anyway, and having the Bluetooth thing built in

We need a powerbank with a built-in Bluetooth to 3.5 mm audio interface. People tend to carry a powerbank around anyway, and having the Bluetooth thing built into it will ensure that this device will never run out of battery. Yes it's going to be a niche product, but some people will love it a lot.