51bk spl

I recently purhased a 1951 Buick special .when I looked @it I hahad the owner start and drive it around the parking lot. He said the battery was shot so he put a jump pack on and it started right up. Idled evenly end seemed to drive decent for a car that old . After it was dropped off I went to move it off the side lawn . And nothing. It cranks has juice to the point but won' even kick with starter fluid any suggestions