After replacing batteries he scales are not working properly. I have changed the batteries three times. My weight registers 72 lbs and I way well over 135. I can hardly get the battery cover back on the scales before the light goes off to get a number to register. After my weight registers inacurately 72 lbs it goes off and will not come back on. I have pulled the back off of these scales countless times to get them to work. Help! My manual is gone.