Hitachi Maxell Ltd on MOnday announced plans to release a wireless battery charger for the iPhone 4. The device is compatible with a standard created by the Wireless Power Consortium (WPC), an industry group related to wireless charging.

The company will release in Japan the "WP-PD10.BK" and the "WP-PD10S.BK" chargers as well as the "WP-SL10A.BK," a sleeve charging case that can wirelessly receive power for Apple iPhone 4. The devices will retail in Japan first and it is not clear whether they will reach other markets.

The WP-PD10.BK can charge two iPhone 4 smartphones at the same time. It has two power transmission units, each of which can transmit power of 5W. The WP-PD10S.BK comes with one power transmission unit and can charge a single device at a time. The WP-SL10A.BK can receive power of 2.5W.



Hitachi-Maxell has not provided manufacturer's suggested retail prices, although they are estimated to be about ¥6,900 (approx US$83.3) and ¥2,900 (approx US$35), for the WP-PD10.BK and the WP-SL10A.BK set, respectively.

The devices are Qi-certified (pronounced "chee") by the Wireless Power Consortium. The Qi standard enables consumer electronic brands and device manufacturers to bring interoperable wireless inductive charging devices to market.

The basic principle of the inductive power transmission is an inductively coupled power transfer system. It consist of a transmitter coil L1 and a receiver coil L2. Both coils form a system of magnetically coupled inductors. An alternating current in the transmitter coil generates a magnetic field which induces a voltage in the receiver coil. This voltage can be used to power a mobile device or charge a battery.