Hailong Ebike battery : is it charging ?

how to know if a Yose Power 'Hailong down tube' type battery is charging.
a quick video as to me it wasn't that obvious (or at least, the basicness of it).
1st go at ebike or ebike kit.
kit involved : Yose Power 15.6ah Battery and 250w front wheel motor.
I think Hailong only make the battery case.