FIG. 1 is a perspective view of an portable backup power supply according to our new design;
FIG. 2 is a front elevational view of the portable backup power supply of FIG. 1;
FIG. 3 is a top plan view of the portable backup power supply of FIG. 1;
FIG. 4 is a bottom view of the portable backup power supply of FIG. 1;
FIG. 5 is a rear elevational view of the portable backup power supply of FIG. 1;
FIG. 6 is a left hand side elevational view of the portable backup power supply of FIG. 1; and,
FIG. 7 is a right hand side elevational view of the portable backup power supply of FIG. 1.
The broken lines which define the bounds of the claimed design form no part thereof.