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557

557 - SMD Battery Holder for A/AA/CR2 Cells | Keystone Electronics

The Keystone Electronics 557 is a surface-mount (SMD/SMT) multiple-cell battery holder designed to accept A, AA, and CR2 size cylindrical cells, supplied on a tape-and-reel tab format for high-volume automated assembly. It is a passive electromechanical component whose sole function is to retain a cell, make reliable electrical contact, and present the cell terminals to the PCB. The holder is built from a tin-plated phosphor-bronze or equivalent spring-alloy contact system housed in a black thermoplastic carrier, giving both mechanical retention and low contact resistance. A battery holder is a passive electromechanical interconnect that provides a user-replaceable power source on a PCB without soldering the cell directly. Battery holders sit one level below PCB interconnects and one level above raw cells in the electromechanical hierarchy: cell -> holder -> PCB interconnect -> board-level power. The 557 specifically targets low-profile surface-mount designs where through-hole holders cannot be used and where a single holder must mechanically accept several common cell sizes for design flexibility. Key features of the 557 include multiple cell-size compatibility (A, AA, and CR2), surface-mount tab terminations for reflow soldering, a thermoplastic carrier rated for typical lead-free reflow profiles, and tape-and-reel packaging for high-speed SMT placement. The tab style terminations eliminate the need for through-hole drilling, reducing PCB fabrication cost and enabling placement on either side of the board. Per the DigiKey listing, the part is shipped as a tab-format SMD holder. The contact system relies on spring tension to maintain contact pressure across the cell's lifetime and over temperature. Because the holder is a mechanical device with no active electronics, electrical performance is characterized primarily by contact resistance, current rating, and mechanical retention force rather than the AC parameters that define active semiconductors. Designers should verify that the holder's rated current exceeds the worst-case load pulse of the host circuit. Typical applications for the 557 include backup power retention on industrial controller boards, RTC and SRAM backup in embedded designs, single-cell memory or real-time-clock hold-up in metering and security equipment, and consumer IoT devices where a user-replaceable coin or cylindrical backup cell is preferred over a hard-to-service board-mounted battery. The CR2 compatibility in particular makes it attractive for compact wireless sensor nodes that need a higher voltage than a coin cell can deliver. When designing in the 557, allow adequate clearance above the holder for cell insertion and removal, and observe the recommended pad footprint and reflow conditions in the Keystone datasheet to avoid solder-joint fatigue. Because the holder is not hermetically sealed, conformal coating or board-level potting may be required in high-humidity environments. This page consolidates distributor pricing, same-family Keystone alternatives, and SMD-vs-THT selection guidance that is not found in the manufacturer datasheet alone.