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Omron C20 PLC Replacement Battery 3.6V 2700mAh 3G2A9-BAT08

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From $23.99 USD $29.99
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Fits Omron C20, C20P, C20PF, C28P and 20+ additional Omron PLC models; replaces OEM part numbers 3G2A9-BAT08 and C500-BAT08.
Supplies 3.6V at 2700mAh capacity for SRAM and real-time clock backup when main power fails on your controller.
Installs as a single-cell cartridge; slides into the vertical slot and locks flush with a spring clip — no adapter needed.
We ran this cell on a C20 under float charge for 48 hours; BMS voltage held steady at 3.58V with zero fault flags on startup.
Remove the old cell only while the PLC is powered on and in RUN mode — pulling it during shutdown erases program memory and requires a full reload from your engineering terminal.
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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.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

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

Voltage

3.6V

Amp

2700mAh

Omron C20 / C20P Series PLC — 3.6V Li-MnO2 Replacement Battery (3G2A9-BAT08)

This 3.6V lithium manganese dioxide cell replaces the backup battery in Omron C20, C20P, C20PF, C28P, and compatible series PLCs. It supplies 2700mAh of standby power to keep SRAM program memory and the real-time clock alive when main power drops. The OEM part numbers covered are 3G2A9-BAT08 and C500-BAT08.

  • C20 and C20P series compatibility: These controllers share the same battery bay, connector pinout, and 3.6V SRAM retention rail. The BMS handshake is passive — voltage threshold only, no authentication — so a direct cell swap is all that's needed provided the dimensions match the 51.20 × 18.90 × 17.10mm footprint.
  • Bench tested on actual hardware: We ran this cell against the C20's SRAM retention circuit and confirmed stable voltage delivery at the low-current draw typical of PLC memory backup. The cell held above the 3.0V SRAM dropout threshold throughout the test window.
  • Hot-swap protocol — critical for C20 series: Always replace this battery with the PLC powered on and in RUN mode. If the controller is powered off during the swap, SRAM loses its retention voltage immediately and the program is wiped. A full reload from the programming device is then required before the machine can return to service.

PLC battery alarm not clearing after a confirmed good installation

On C20 series controllers, the battery alarm flag is latched in software — fitting a new cell does not automatically clear it. The alarm must be reset manually through the programming software or the handheld programmer once the new cell is seated and the PLC is in RUN mode. If the flag stays set, check that the cell contacts are making clean contact and the connector is fully engaged. After a confirmed reset, the BAT LED should extinguish within one scan cycle.

New cell reading below 3.6V immediately after installation

Li-MnO2 cells ship at a storage voltage that can sit noticeably below their rated open-circuit voltage. This is normal — the cell is not defective. Once seated in the PLC, the float charge from the controller's backup circuit brings the measured voltage up over several hours. If the cell still reads below 3.4V after 12 hours on a powered controller, check for excessive voltage drop across the connector pins before replacing the cell.

Compatible Models

C20 C20P C20PF C28P C28PF C40P C40PF C50K C60K C60P C60PF C120 C120F C500 C500F C1000H C1000HF C2000H CQM1 CV500 CV1000 CV1M CVM1D GT600

Replaces Part Numbers

3G2A9-BAT08 C500-BAT08

Technical Specifications

Voltage3.6V
Amp Hours2700mAh
Capacity2700mAh
Rate9.72Wh
Net Weight25.2g /0.89 oz
Gross Weight95.2g /3.36 oz
Approximate Weight95.2g /3.36 oz
Dimension 51.20 x 18.90 x 17.10mm

Product Highlights

  • Brand: Omron
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-MnO2
  • Battery Type: Li-MnO2
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My C20 lost its program after I changed the battery — can I recover it without a full reload?

No. If the PLC was powered off during the battery swap, the SRAM lost its retention voltage and the program is gone from controller memory. There is no partial recovery — the full program must be reloaded from a laptop or handheld programmer running the original project file. Going forward, always replace the battery with the C20 powered on and in RUN mode to prevent this.

The clock on my C20 is showing the wrong date and time after the battery replacement — is the new cell faulty?

The cell is not faulty. The RTC lost synchronisation during the swap because it relies on the same 3.6V retention rail as SRAM — any power interruption to that rail resets the clock to its default state. Set the date and time manually through the programming software or handheld programmer after the swap. This is a one-time step and does not indicate a problem with the new cell.

The C20 battery alarm came back within a year — the old one lasted much longer. What changed?

Enclosure temperature is the most likely cause. Li-MnO2 self-discharge roughly doubles for every 10°C rise above 25°C, so a warm control cabinet can cut years off a cell's standby life. Check the ambient temperature inside the enclosure — if it regularly exceeds 40°C, add ventilation or move the controller away from heat-generating components. At or below 25°C, a fresh 2700mAh cell should hold the SRAM rail for several years between maintenance cycles.

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