Qi Wireless Charger Receiver Back Case for Iphone 4 / 4s (White) Designed for iPhone 4 / 4S Qi wireless charging receiver back case. Works with All WPC Qi Wireless Charger Dock / Wireless Charging Pad. Charging distance: 3-7mm, Input Power: 5W, Charging current: 600mA. Working Frequency: 100-200KHz, Charging effeciency: &gt;72%, Charging time: 4  0.5 hrs Built-in Qi wireless receiver module latest improved chip, High Wireless Charging efficiency.