The ornamental design for a flatbatterypack, as shown and described.
FIG. 1 is a top, front, right side perspective view of a flat battery pack of our new design;
FIG. 2 is an enlarged view of the identified portion of FIG. 1;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is an enlarged view of the identified portion of FIG. 4;
FIG. 6 is a left side elevation view thereof;
FIG. 7 is a right side elevation view thereof;
FIG. 8 is a rear elevation view thereof;
FIG. 9 is a front elevation view thereof; and,
FIG. 10 is an enlarged view of the identified portion of FIG. 9.
The broken line rectangles in FIGS. 1, 2, 4, 5, 9, and 10 are for the purpose of illustrating the bounds of the portions shown enlarged in the views. The remaining broken lines are for the purpose of illustrating portions of the article that form no part of the claimed design.