The cell phone battery has a master chip that controls the current and voltage. Some battery protection is also included. He will check the battery's power and temperature, too high temperature will reduce the current and voltage, and the charging speed will be normal when the temperature is normal. Therefore, charging while playing can be very slow. Charging time is too long or playing while charging will not have much impact on the battery, now the mobile phone is a year to change, the battery is not bad was taken to sell second-hand, do not worry