The MiLi will accompany you and your iPhone through great and wonderful times -- you can enjoy your movies, music, phone call and internet surfing. You will never worry about shortage of battery power when enjoying the iPhone's colorful features. MiLi Power Pack is compatible with iphone 4. You can use the included USB cable to charge the MiLi Power Pack. When the iPhone is securely placed in the MiLi and connected to an electrical power source, the iPhone will be firstly charged until full, then the Power Pack next. Press the power button to start charging in condition of no external electrical source connected. MiLi Power Pack will stop charging automatically when iPhone is fully charged. Press the power button or connect with electrical source if recharge in need. Remarks: Please use Apple original charger, PC or MiLi charger to charge MiLi Power Pack. When using the MiLi Power Pack with your iPhone, you can sync your iPhone with iTunes without removing the MiLi Power Pack.