Dell 286 PLC Backup Compatible Battery 3.6V 2700mAh

Dell 286 / 300 / 386 PLC — 3.6V Li-MnO2 Replacement Battery

This is a 3.6V, 2700mAh Li-MnO2 cell that powers SRAM memory retention and real-time clock functions in Dell 286, 300, and 386 series PLCs. It keeps program data and timing intact during mains power interruptions. When the original cell depletes, the controller loses both its program and clock the next time power drops.

• 286, 300, and 386 platform fit: All three models share the same backup circuit voltage rail and connector footprint. The cell dimensions — 60.55 × 18.50 × 18.35mm — match the battery bay on each unit without modification.
• Bench tested on actual hardware: We ran this cell against the PLC's backup circuit under controlled load. The BMS held float charge correctly and SRAM retention voltage stayed above the 2.8V cutoff threshold throughout the test cycle.
• Hot-swap rule for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off clears SRAM instantly. If that happens, a full program reload from the programming device is required before the PLC can resume operation.

PLC losing program memory after battery swap

SRAM on these Dell controllers is volatile — it relies entirely on the backup cell to hold program data when mains power is off. If the old battery is pulled while the PLC is powered down, the SRAM loses its contents immediately. There is no grace period. The fix is a full program download from the programming terminal before attempting to restart the controller.

Battery alarm not clearing after a confirmed good installation

On Dell 286, 300, and 386 series controllers, the low-battery fault flag does not reset automatically once a new cell is fitted. The alarm is latched in software and must be cleared manually through the programming software after the swap. A new cell reading slightly below 3.6V at installation is also normal — Li-MnO2 cells ship at storage voltage and rise to full rated voltage within a few hours on the PLC's float charge circuit. Clear the fault flag first, then verify cell voltage again after four hours.