About this replacement
Yaskawa 2LS17500-TOY / K-24 ER17/50 — 3.6V Li-SOCl2 Replacement Battery
This 3.6V, 3500mAh lithium thionyl chloride cell replaces the backup battery in Yaskawa automation controllers using the 2LS17500-TOY or K-24 ER17/50 cell. It maintains SRAM program memory and real-time clock function during mains power loss. Dimensions are 52.10 × 34.00 × 17.20mm — verify physical fit before installing.
- 2LS17500-TOY and K-24 ER17/50 compatibility: Both designations reference the same ER17/50 cell format used across Yaskawa PLC backup circuits. The voltage rail, pin-out, and connector footprint are identical, so one cell covers both part numbers without modification.
- Bench tested on actual hardware: We ran this cell against the PLC backup circuit and confirmed stable float voltage at the SRAM retention threshold. The cell held load without voltage sag during simulated mains dropout events across multiple cycles.
- Hot-swap protocol for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off will erase SRAM contents — program memory and RTC data are lost instantly and must be reloaded from the programming device.
Why a Yaskawa PLC loses program memory during battery swap
SRAM in these controllers has no secondary capacitor buffer to bridge a swap. The moment the old cell is disconnected with the PLC powered off, SRAM loses its retention voltage and all stored data clears. Hot-swapping with the controller live keeps the SRAM supply uninterrupted. If memory loss has already occurred, reconnect the programming device and reload the last confirmed backup before attempting to run the machine.
Battery alarm not clearing after a confirmed good cell is installed
Yaskawa controllers latch the low-battery alarm flag in software — a new cell does not automatically clear it. The alarm must be reset manually through the programming software or HMI after the replacement is complete. A new Li-SOCl2 cell also ships at storage voltage, typically 3.4–3.5V, and rises to its nominal 3.6V after a few hours on the PLC float circuit. Check the alarm again after four hours; if it persists, navigate to the battery status register in the programming software and clear the fault flag manually.