[DrBob]

The battery box bottom is held shut by two good sized bolts. The only way to have it come open is if those two bolts both fall out because they were not tightened when the battery was put in, or if the hinge in the front of the box breaks.
This is a good lesson- to prevent dangerous problems, everyone should give thier bike a once over every now and then, looking for loose bolts and metal fatigue.