we buy this for my teenage son , who be want to know how far he would run each day . after 2 month , he have be able to use it 3 time . it will not keep a charge . I charge it and by the next time he want to use it , it be not charge anymore . and of course , when I go to see about return it , Amazon say that we can not because the return window be go . not good . still have to get in touch with customer service , and hopefully they can give I some guidance for use it and a way to keep the charge .