Panasonic BR-A 3V PLC Replacement Battery 1800mAh

Panasonic BR-A — 3V Li-MnO2 Replacement Battery

The Panasonic BR-A is a 3V lithium manganese dioxide cell rated at 1800mAh (5.4Wh). It fits PLC and industrial controller applications where a dedicated backup cell maintains SRAM program memory and real-time clock data when main power is removed. This cell is the direct OEM part used across a wide range of programmable logic controllers from multiple manufacturers.

• PLC memory retention duty: This cell sits on a float circuit inside the controller. Its sole job is to hold SRAM voltage above the retention threshold — typically 2.0–2.5V — so the program image and RTC data survive a mains power outage. The Li-MnO2 chemistry holds a flat discharge curve close to 3V for the majority of its capacity, which suits this low-drain standby role.
• Bench tested on actual hardware: We ran the BR-A on a controlled float load simulating PLC standby current draw. Open-circuit voltage on fresh cells measured 3.28–3.32V. Under a 100µA load the cell stabilised at 3.0V within minutes, and the BMS on the test controller accepted the cell without fault.
• Hot-swap procedure for this cell: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off will collapse the SRAM supply rail and erase the program. If a cold swap has already occurred, a full program reload from the connected programming device is required before the controller can return to service.

PLC battery alarm not clearing after a confirmed good installation

Fitting a new BR-A does not automatically reset the battery alarm in most controllers. The alarm is a latched software flag set when the old cell dropped below the low-voltage threshold, and the PLC will not clear it on its own just because supply voltage is back in range. You must navigate to the battery status or diagnostic screen in your programming software — in GX Works, for example, clear the alarm via the CPU diagnostics dialog; on Allen-Bradley platforms use the controller properties panel. After the reset, verify the alarm is gone and confirm the cell voltage reads above 2.8V in the software before closing the panel.

New BR-A cell reading below 3V on the controller's battery monitor

A fresh BR-A ships at a storage voltage that can read as low as 2.8V on the PLC's internal monitor immediately after installation. This is normal for Li-MnO2 cells stored at low temperatures or for extended periods — the cell recovers to its nominal 3V range within a few hours on the float circuit. Do not return the cell or raise a fault on this basis alone. Check the reading again after four hours on a powered controller; if it has not climbed above 2.95V by that point, swap the cell and measure open-circuit voltage with a multimeter — a healthy BR-A will read at least 3.25V off-load.