A large round baler includes a pair of ground wheels carried at opposite ends of an axle which is suspended from the frame of the baler by a pair of parallel, transversely spaced arms having first ends secured to the axle, and having second ends coupled to the frame by a self-aligning bearing assembly. Such increase of intensities improves effectiveness of critical openings that are otherwise too small to print. Besides, a constant current is provided to charge the battery, and when a terminal voltage of the battery reaches to a charging preset voltage, a constant voltage is provided to charge the battery.