About this replacement
Maxell ER6 — 3.6V Li-SOCl2 Replacement Battery
This is a 3.6V, 2000mAh lithium-thionyl chloride cell that replaces the Maxell ER6 in PLCs and industrial automation controllers. It provides backup power for SRAM memory retention and real-time clock functions when mains power is interrupted. Dimensions are 54.34 × 14.10 × 14.10mm — confirm these match your existing cell before installing.
- PLC backup power role: The ER6 does not run the PLC — it holds SRAM contents and RTC timing during power outages. Without it, the controller loses its program and clock data the moment mains power drops.
- Bench tested on actual hardware: We measured open-circuit voltage at delivery, verified stable float behaviour at 3.6V, and confirmed the cell holds retention voltage under the low-microamp draw typical of PLC backup circuits.
- Hot-swap rule for PLC installation: Always replace this cell with the PLC powered on and in RUN mode. Removing the old cell while the controller is powered off will cause SRAM loss — the program will be gone and must be reloaded from a programming device.
PLC battery alarm not clearing after a confirmed good installation
Most PLCs do not reset the battery alarm automatically when a new cell is fitted. The alarm is a latched fault that must be cleared manually through the programming software — typically via the diagnostics or status buffer. On Siemens S7 controllers, this is done through STEP 7 or TIA Portal by acknowledging the battery fault in the module properties. Allen-Bradley controllers generally require a similar manual clear through RSLogix or Studio 5000.
New ER6 cell reading below 3.6V straight out of packaging
Li-SOCl2 cells ship in a passivation state — the internal lithium surface develops a thin film during storage that temporarily suppresses open-circuit voltage. A fresh ER6 may read as low as 3.2V on a multimeter before installation. Once seated in the PLC and drawing the low microamp standby current, the passivation layer breaks down and voltage rises to full rated output within a few hours. No action is needed beyond installing the cell and allowing time for recovery.