iPad Pro charging from external battery

Assuming that the tags appended to your post are correct (iPad Pro 11”?), whilst lacking detailed information as to what you are attempting to connect to your iPad...

If attempting to use a PowerBank Battery that presents a standard USB Type-A connection - then to connect with your iPad Pro, you will require a USB-Type A to USB-C cable. These are readily available from good retailers. Here is one example marketed by Apple:

• mophie USB-A Cable with USB-C Connector (1 m)

https://store.apple.com/uk/xc/product/HN892ZM/A

By contrast, if your PowerBank presents a USB-C connection, you will instead require a USB-C to USB-C cable. Again, these are readily available from good suppliers. Here is Apple’s own cable:

• USB-C Charge Cable (1m)

https://store.apple.com/uk/xc/product/MUF72ZM/A

You are very welcome.

All models of iPad can be charged from a suitable AC Power Adapter or Battery PowerBank. If the Power Adapter or PowerBank support USB PD (Power Delivery), your iPad Pro can continue to benefit from Fast Charging. You simply require the appropriate cable.

Please be assured your assessment is purely your interpretation - and was was not intended as such.

As a postscript, in making further assumption that your PowerBank battery has a standard USB Type-A connection, be aware that (a) it must be able to provide at least 10-12W output to reliably charge an iPad - and (b) USB PD Fast Charging will not be available.

Fast Charging is only implemented with USB PD-compliant power sources over USB-C connections.