Yes, long-term use is harmful, because the negative charger is not the same.
May damage the battery: Apple phone charger output, most are 5v and 1A, 5v represents the charger can output stable DC voltage, 1A refers to the output current, if the use of non-original charger, current output is too large or too small, are easy to damage the battery. May not be able to charge: after ios7 system, Apple mobile phone has opened the data line certification standard, some non-original chargers may lead to the phone can not charge, need to be replaced. It is recommended to use the original, if you want to use non-original, please also select the appropriate current input to use again.