Video monitor question

SkiHorse

Anyone have the Summer Infant Slim & Secure Video monitor? 

If so, maybe you can answer a question about it:  It has a green light that indicates whether the battery is charged. It looks like the light ought to be a  "bar graph" display that shows how fully charged the battery is.  But even after charging ours for double the time required by the instructions, only a couple of bars seem to light up, rather than a whole row.  Is that normal? Or do we have a dud?