USB socket charging the phone is not harmful to battery life. Mainly because the output current of the USB socket can not reach the current voltage of the charger. The charging current of the USB socket is relatively small and the charging time is relatively long, but the small current is not easy to damage the battery life. So USB socket charging mobile phone battery is still OK. Is a little longer, will not damage the battery life, this point is more good, I hope my answer can help you.
No, but it will affect the phone system. And charging is very slow. USB charging is not recommended