I have a question about external battery packs. I just got the HIBOY Max for commuting to work. I rode it in for the first time which is about 7.5 miles From where I live. I noticed that once the battery gets down to a certain percentage the scooter only goes 12-15mph. I would rather do 18mph the whole way. So I am trying to find a External Battery pack that will fit the Hiboy Max.