Power Bank

1. Power bank 1 . 1 is a top, front and left perspective view of a power bank showing my new design; 1 . 2 is a front elevational view thereof; 1 . 3 is a rear elevational view thereof; 1 . 4 is a left side view thereof; 1 . 5 is a right side view thereof; 1 . 6 is a top plan view thereof; and 1 . 7 is a bottom plan view thereof. The broken lines in the drawings illustrate portions of the power bank which form no part of the claimed design.