How long can camera record if it's connected to mobile powerbank?

That depends upon an important specification you’ve failed to provide: what is the power consumption of the unit? 

Depends on whether the camera has its own storage or whether its output is connected to an external storage device such as a hard drive, how big the hard drive is and how much current does the camera draw

Four factors in determining the amount of time a camera can record:

1) The length of time it takes for the camera to overheat.  This is most applicable to digital cameras that were not designed as video devices such as a DSLR.  If the camera is of poor quality, it can overheat, too.

2) The size of the memory card.

3) The resolution of the recording.

4) How much power it draws in conjunction with the life of the battery.  See if you can hard-wire the camera to an outlet.

The best answer will likely come from a user or from the manufacturer's tech support.  I would call them and have the size of the card available.

That depends upon an important specification you’ve failed to provide: what is the power consumption of the unit? 

Try it and see...it's more likely to run out of storage before the battery goes flat.