486DX33 Industrial PLC Replacement Battery 3.6V 2700mAh

Comtrade 486DX33 — 3.6V Li-MnO2 Replacement Battery

This 3.6V, 2700mAh lithium-manganese dioxide cell replaces the backup battery in 486DX33-based industrial controllers and PLCs. It maintains SRAM program memory and real-time clock data during mains power loss. Without a healthy cell, the controller loses its program and clock the moment power is cut.

• 486DX33 platform fit: These controllers use a dedicated backup rail at 3.6V nominal to sustain SRAM and RTC circuits independently of the main supply. The cell dimensions — 60.55 × 18.50 × 18.35mm — match the original holder footprint, and the Li-MnO2 chemistry matches the low self-discharge profile the platform expects over long standby intervals.
• Bench tested on actual hardware: We confirmed BMS behaviour under float conditions and verified the cell holds its open-circuit voltage within spec across the expected standby load. The backup rail draw on this class of controller is measured in microamps, so cell chemistry and capacity stability matter more than peak output.
• Hot-swap protocol for 486DX33 controllers: Always replace this cell with the controller powered on and in RUN mode. Removing the battery while the PLC is powered off will wipe SRAM instantly — the main supply is the only thing protecting memory during the swap. If the controller was off during the change, a full program reload from the programming device is required before returning to service.

PLC losing program memory after battery swap

On 486DX33-based controllers, SRAM is not flash — it holds data only while at least one voltage source is present on the backup rail. The moment both the main supply and the battery are absent simultaneously, the memory array clears completely. This happens in under a millisecond, so even a quick cell swap with the PLC off is enough to cause a full memory loss. Reconnect mains power, reload the program from your programming device, and verify the RTC is set correctly before returning the machine to service.

Battery alarm not clearing after a confirmed good installation

Fitting a new cell does not automatically clear the battery alarm on most 486DX33-platform controllers — the fault flag is latched in software and must be reset manually. Open your programming software, navigate to the diagnostics or status register for the battery fault bit, and clear it explicitly. If the alarm returns within minutes of clearing, measure the cell's open-circuit voltage with a multimeter before condemning the installation — a freshly shipped Li-MnO2 cell may read slightly below 3.6V until it has been on the PLC's float charge for a few hours.