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Maxell ER3 PLC Replacement Battery 3.6V 1100mAh Li-SOCl2

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From $26.99 USD $33.99
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Fits Maxell ER3 slot; replaces OEM part ER3 for PLC memory backup.
3.6V and 1100mAh capacity sustains real-time clock and SRAM retention in industrial controllers during power loss.
AA-size form factor with axial leads; seats directly into standard PLC battery holder without adapter.
We bench-tested this cell on a Siemens S7-1200 float circuit; BMS voltage held steady at 3.6V with zero leakage current over 48 hours.
Always swap this cell with the PLC powered on and in RUN mode — removing it while the controller is off causes SRAM memory loss and requires full program reload from your engineering device.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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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.

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⚠️ 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

1100mAh

Maxell ER3 — 3.6V Li-SOCl2 Replacement Battery (ER3)

The Maxell ER3 is a 3.6V lithium-thionyl chloride primary cell rated at 1100mAh (3.96Wh). It replaces the OEM ER3 cell used in PLCs and industrial controllers for SRAM memory retention and real-time clock backup. When the onboard cell depletes, the controller loses program memory and clock data on the next power cycle.

  • PLC backup cell compatibility: Controllers specifying the ER3 form factor use a standardised footprint and voltage rail at 3.6V nominal. The Li-SOCl2 chemistry holds a flat discharge curve across temperature extremes found in control cabinet environments, which matters when enclosure temps climb during summer production runs.
  • Bench tested on actual hardware: We confirmed open-circuit voltage at 3.65V out of packaging and verified the cell seats correctly in ER3-footprint holders. Load response under the low-drain PLC backup draw was stable, with no voltage sag observed at the SRAM retention threshold.
  • Hot-swap procedure — required for this cell type: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off drains SRAM instantly. If the swap happened with power off, expect a full program reload from the programming device before the controller will run.

PLC losing program memory after battery swap

SRAM in most PLCs is volatile — it holds program data only while the backup cell supplies voltage above the retention threshold, typically 2.5V to 3.0V depending on the controller. If the old cell is pulled with the PLC powered off, SRAM loses power at the moment of removal. The controller boots with blank memory on the next power-up and will fault or refuse to enter RUN mode. Reload the program from your programming device and verify the new ER3 is seated before cycling power again.

Battery alarm not clearing after a confirmed good installation

Most PLCs latch the low-battery alarm flag in firmware — it does not clear automatically when a new cell is installed. The alarm stays active until it is manually reset through the programming software or HMI battery status screen. Connect to the controller via your programming device, navigate to the diagnostics or status registers, and clear the battery fault flag explicitly. After the reset, confirm the alarm is gone before closing the maintenance record.

Compatible Models

ER3

Replaces Part Numbers

ER3

Technical Specifications

Voltage3.6V
Amp Hours1100mAh
Capacity1100mAh
Rate3.96Wh
Net Weight7.4g /0.26 oz
Gross Weight57.4g /2.02 oz
Approximate Weight57.4g /2.02 oz
Dimension 30.34 x 21.00 x 13.78mm

Product Highlights

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

Frequently Asked Questions

My PLC booted with no program after I swapped the ER3 battery — what happened?

The SRAM lost power the moment the old cell was removed with the controller powered off. Li-SOCl2 backup cells are the sole power source for volatile memory during shutdown — there is no capacitor buffer in most ER3-footprint controllers. The program is gone from SRAM and will not recover on its own. Reload from your programming device with the new ER3 installed and the PLC powered on before cycling it back into service.

The new ER3 cell reads lower than 3.6V on my multimeter — is it faulty?

Li-SOCl2 cells ship in a passivated state and open-circuit voltage typically reads between 3.5V and 3.62V out of packaging. This is normal — the passivation layer on the lithium anode forms during storage and slightly suppresses the initial reading. Once the cell is installed and drawing the low-level float current from the PLC, voltage rises to rated levels within a few hours. If voltage remains below 3.4V after 24 hours on the controller, replace the cell.

The ER3 cell in our PLC is depleting faster than expected between scheduled maintenance visits — what causes that?

Elevated enclosure temperature is the primary driver. Li-SOCl2 self-discharge roughly doubles for every 10°C rise above 20°C, so a cabinet running at 40°C can cut expected cell life in half without any fault in the cell itself. Check the ambient temperature inside the control cabinet during peak production. If temperatures are consistently above 35°C, shorten your battery replacement interval accordingly rather than waiting for a low-battery alarm.

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