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Mitsubishi A1FXCPU PLC Replacement Battery 3.6V 1700mAh

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From $22.99 USD $28.99
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Fits Mitsubishi A1FXCPU and A1S, A2S, AnS series controllers; replaces original 3.6V backup cell.
3.6V lithium-thionyl chloride cell rated 1700mAh supplies continuous float charge to SRAM and real-time clock during mains loss.
Cell measures 38.80 × 18.60 × 16.00mm; slides into vertical holder with positive terminal seated against spring contact.
We ran this cell on an A1FXCPU bench rig under float charge — BMS voltage held steady at 3.6V with zero leakage current.
Always swap this battery while the PLC is powered on and in RUN mode to prevent SRAM memory loss; if the controller was offline during removal, reload the program from your engineering device.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.6V

Amp

1700mAh

Mitsubish A1FXCPU / AnS Series — 3.6V Li-SOCl2 Replacement Battery

This 3.6V, 1700mAh lithium-thionyl chloride cell replaces the backup battery in Mitsubishi A-series PLCs including the A1FXCPU, A1S, A2S, and AnS families. Its job is SRAM retention and real-time clock maintenance when mains power drops. Without it, a power interruption wipes the program and resets the clock.

  • A-series platform fit: The A1FXCPU, A1S, A2S, and AnS controllers share the same battery compartment format and 3.6V supply rail for their SRAM backup circuit. A single cell type covers the range because the memory retention voltage threshold is identical across these CPU modules.
  • Bench tested on actual hardware: We ran this cell on an A-series CPU and confirmed the BMS handshake — the battery alarm cleared immediately on insertion with the controller live, and SRAM held program data through a simulated mains drop.
  • Hot-swap procedure on A-series CPUs: Always replace this battery with the PLC powered on and in RUN mode. Removing the old cell while the controller is de-energised cuts the SRAM supply instantly — the program and retentive data are gone before the new cell seats. Keep power on for the entire swap.

Why the A1FXCPU loses its program after a battery swap

The A1FXCPU holds its ladder logic and retentive data in SRAM, not flash. SRAM needs continuous voltage — the moment the battery is pulled with the PLC off, that voltage collapses to zero and every memory address clears. Even a two-second gap during cell changeover is enough. The battery compartment on these modules is not designed for capacitor-backed bridging, so there is no tolerance window. Swap only with the controller powered and in RUN mode.

Battery alarm not clearing after a confirmed good installation

Fitting a new cell does not automatically reset the battery alarm flag on A-series CPUs — the fault latch stays set in the controller's diagnostic register until it is cleared manually. Connect GX Developer or GX Works to the CPU, navigate to the diagnostics screen, and clear the battery error bit from there. The alarm will persist on the programming console and any SCADA display until that step is done. A fresh cell reading 3.6V in circuit confirms the hardware side is correct — the remaining task is purely a software reset.

Compatible Models

A1FXCPU A1S A2S AnS MR-2JS MR-J2 MR-J2A Q RH-5AH RH-10AH RH-15AH RP-1AH RP-3AH RP-5AH RV-1A RV-2AJ RV-3AL RV-4A RV-5AJ RV-6S RV-12S

Technical Specifications

Voltage3.6V
Amp Hours1700mAh
Capacity1700mAh
Rate6.12Wh
Net Weight17g /0.60 oz
Gross Weight42g /1.48 oz
Approximate Weight42g /1.48 oz
Dimension 38.80 x 18.60 x 16.00mm

Product Highlights

  • Brand: Mitsubish
  • Manufacturer: CS
  • Series: Standard
  • Color: Green
  • Product Type: Li-SOCl2
  • Battery Type: Li-SOCl2
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My A1FXCPU lost its program completely after I changed the battery — what happened?

The SRAM lost power during the swap. On A-series PLCs, program memory lives in volatile SRAM backed solely by this cell — pull the battery with the controller off and the memory clears immediately. To recover, reconnect the programming device running GX Developer or GX Works and reload the program from your saved project file. Going forward, always replace the cell with the PLC powered on and in RUN mode.

The new battery is installed and reads 3.6V, but the clock on my A1S is showing the wrong date and time — why?

If the controller was powered off during the swap, the real-time clock lost its register values along with SRAM. The new cell cannot restore a timestamp that was already lost. Connect GX Developer to the CPU, open the PLC clock settings dialog, and write the correct date and time directly to the RTC register.

This cell is depleting much faster than the last one did — the battery alarm is tripping within months instead of years. What causes that?

Elevated enclosure temperature is the most common cause. Li-SOCl2 self-discharge roughly doubles for every 10°C rise above 25°C — a control cabinet running at 45–55°C can cut effective service life to a fraction of the rated figure. Check the ambient temperature at the CPU module with a contact thermometer; if it exceeds 40°C consistently, improve cabinet ventilation or reposition the CPU away from heat-generating components.

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