Basically as the title says. We have semi frequent power outages where I live. The noise machine in my daughter’s room goes out and wakes her up. If I were to buy a USB powered one, plug it into a power bank like one of those 10000ma ones you get for charging cell phones, would it have continuous power. Basically like a cheap UPS
As long as the battery bank supplies sufficient power continuously, it would certainly power it! If it doesn’t, you’d have to look at a battery bank to power the device but I’d bet your daughter’s noise machine is likely going to work fine on anything.
However, skatrek47 brings up a good point: The battery would need to just be powering the machine (unless you had an automatic cutover, but that seems like overkill for this application).
For your use case, I’d say just run it off the battery all the time and charge it once the battery gets around 20%.
There’s USB batteries that’ll do passthrough charging too, but keeping a battery charged all the time will kill it, so you might as well just use the battery.
If you wanted to go nuts, you could get an APC or something but that would be pretty silly for this.