Fanuc A98L-0031-0026 PLC Backup Compatible Battery 3V 1750mAh

Fanuc A02B-0309-K102 — 3V Li-MnO2 Replacement Battery (A98L-0031-0026)

This is a 3V lithium manganese dioxide cell rated at 1750mAh, built to replace the A98L-0031-0026 in the Fanuc A02B-0309-K102 PLC. It supplies backup power to the controller's SRAM and real-time clock, keeping stored programs and system time intact when mains power drops. Swap it before the low-battery alarm escalates to memory loss.

• A02B-0309-K102 backup circuit: The Fanuc A02B-0309-K102 uses a dedicated 3V lithium cell to hold SRAM state and RTC data independently of the main power supply. The cell floats across the backup rail at a fixed voltage — a mismatch in cell chemistry or voltage causes the BMS to reject the source and log a battery fault immediately.
• Bench tested on actual hardware: We ran this cell against the A02B-0309-K102 backup rail and confirmed the BMS accepted the cell without fault. The RTC held sync and SRAM retention remained active throughout the load cycle with no voltage drop events recorded.
• Hot-swap procedure for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off will wipe SRAM instantly — stored programs and parameters are gone. If the PLC was off during the swap, a full program reload from the programming device is required before restarting production.

PLC battery alarm not clearing after a confirmed good installation

Installing a fresh cell does not automatically clear the battery alarm on the Fanuc A02B-0309-K102. The alarm flag is written to a register in the controller's diagnostic memory and must be reset manually through the programming software. Navigate to the alarm or diagnostic screen in the Fanuc interface and perform a manual alarm clear after confirming the cell is seated and the voltage reads 3V. If the alarm returns within minutes, check the cell contacts for oxidation — a resistive connection prevents the controller from seeing a valid voltage source.

New cell reading lower than 3V on the controller's diagnostic screen

Li-MnO2 cells are shipped at a storage voltage slightly below their rated terminal voltage. Once seated in the PLC, the backup circuit applies a float charge and the cell stabilises to its full 3V within a few hours. Do not pull and replace a new cell based on a low reading taken immediately after installation. Check the diagnostic screen again after four hours of powered operation — if voltage has not recovered to at least 2.8V by that point, the cell or the backup circuit contacts need inspection.