Abstract: A robust system, apparatus, and method for precise in-house positioning utilizing RFID (Radio Frequency Identification) technology are described in this invention. The in-house environment is partitioned into separate locations, and a set of RFID tags are scattered in the environment. Reading patterns of RFID tags are collected at each location by an RFID reader as samples. Pattern recognition and classification methods are used, when human, vehicle, or other carrier move around the environment with an RFID reader to estimate its physical location based on the reading pattern. The precision can be within one meter. The method is adaptive to different tag distribution, reader range, defective tags, and other physical constraints.

Abstract: A battery charger has at least one seat, a charging slot with an interior step configuration to divide the charging slot into two plug-in regions. A circuit device is installed in the seat. The circuit device has at least one conductive terminal, which has to contact parts located at two plug-in regions. The charger further has a positioning base for mounting the seat thereon. By forming two charging slots with each two plug-in regions, the charging slot allows two batteries with different sizes and specifications to be charged at the same time. As the positioning base is easily fabricated with various dimensions, the battery charger can be expanded with a plurality of charging slots. In addition, the charger is easily assembled and utilized.