A Battery Powered Lightening - USB Adapter - For Thumb Drives

[roystreet]

OK, my question arises from the fact that the iPad 12.9 (2nd gen) still uses lightening and doesn't have the power like the USB C has. I have an adapter that I can plug into my iPad and plug a power supply into it and it can read many thumb drives. But, being on the go, I don't want to have to plug the adapter to a outlet or a separate battery supply. Do any of you know of an adapter that has a battery built into it already?

I hope I'm not confusing here.