Battery external connection device for use with mobile phone and flip cover having the device

A flip cover applying to a mobile phone and having a battery external connection device includes a front unit and a rear unit connected to the front unit and is characterized by: an ultra-thin rechargeable battery; the front unit having therein a sandwich space for accommodating and thereby storing the ultra-thin rechargeable battery; the rear unit having thereon a battery external connection device and functioning as a back cover of the mobile phone to substitute for an original back cover of the mobile phone; a battery external connection device including a first electrical connection terminal and a second electrical connection terminal which are electrically connected to a positive pole and a negative pole of the ultra-thin rechargeable battery, respectively.