A portable battery charger has a built-in, retractable connector for charging a portable electronic device. This new and distinct variety has shown to be uniform and stable in the resulting generations from asexual propagation. The stent may have a radially compressed configuration and a radially expanded configuraton, in which the first section has a first shortening ratio, and the second section has a second shortening ratio less than the first shortening ratio. As a result, the digital signal processor according to the present invention has less connecting terminals and achieves a size reduction.