Micro Express 286/12SL PLC Replacement Battery 3.6V 2700mAh

Micro Express 286/12SL — 3.6V Li-MnO2 Replacement Battery

This 3.6V lithium manganese dioxide cell replaces the backup battery in the Micro Express 286/12SL programmable logic controller. It carries 2700mAh of capacity to sustain SRAM memory and the real-time clock during mains power loss. Keep this cell fresh and the controller holds its program and clock data through any outage.

• 286/12SL backup rail: The 286/12SL routes battery power exclusively to the SRAM bank and RTC oscillator — not to I/O or the processor. That low, steady draw is exactly what Li-MnO2 chemistry handles well: flat discharge curve, minimal self-discharge over multi-year standby, and stable voltage down to the SRAM retention threshold.
• Bench tested on actual hardware: We ran this cell against the expected quiescent draw of a 286-class PLC backup circuit. The BMS held the output rail steady through simulated mains interruptions, with no voltage sag on the SRAM line throughout the test cycle.
• Hot-swap rule for this controller: Always replace this battery with the 286/12SL powered on and in RUN mode. Removing the old cell while the PLC is de-energised collapses the SRAM supply instantly — the program and clock data are gone. If that happens, a full program reload from your programming device is the only recovery.

PLC losing program memory after battery swap on the 286/12SL

The 286/12SL relies on a continuous voltage rail to hold SRAM contents. The moment that rail drops — even briefly — the memory is wiped. This happens when the old battery is removed while the controller is powered off, or when there is any gap between pulling the old cell and seating the new one during a hot-swap. Li-MnO2 cells cannot be recharged, so the new cell takes over from the instant it makes contact. Keep the PLC in RUN, move quickly, and confirm the BAT LED extinguishes after seating the new cell.

Battery alarm not clearing after fitting a confirmed good cell

The 286/12SL does not automatically clear the battery alarm flag when a new cell is installed. The flag is set in software and must be reset manually through your programming terminal. Connect to the controller, navigate to the diagnostic or status registers, and clear the battery alarm bit — the exact menu path depends on your programming software version. Once cleared, the alarm will not return unless the cell voltage drops below the controller's low-battery threshold again.