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Maxell ER17/33 PLC Replacement Battery 3.6V 1600mAh Li-SOCl2

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Fits Maxell ER17/33 PLC backup cells; direct OEM part number replacement for programmable logic controllers.
3.6V lithium thionyl chloride cell rated 1600mAh — supplies memory retention and real-time clock power to PLC systems.
Cylindrical AA form factor; slides into vertical or horizontal PLC battery socket with spring contact retention.
Bench testing on Siemens S7 and Allen-Bradley platforms confirmed stable float voltage acceptance; BMS-free primary chemistry eliminates handshake faults.
Install this cell only while the PLC is powered on and in RUN mode — removing it during controller shutdown causes immediate 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

1600mAh

Maxell ER17/33 — 3.6V Li-SOCl2 Replacement Battery (ER17/33)

This is a 3.6V, 1600mAh lithium thionyl chloride primary cell. It replaces the Maxell ER17/33 backup battery used in PLCs and industrial controllers to retain SRAM program memory and keep the real-time clock running when main power is removed. Capacity is 1600mAh (5.76Wh) as specified in the product data.

  • PLC memory backup application: These cells share a common voltage rail requirement — the controller's SRAM and RTC circuits draw a standby current in the low-microamp range, and the Li-SOCl2 chemistry holds a stable 3.6V across that load for the full cell life without the voltage sag you get from alkaline or NiMH alternatives.
  • Bench tested on actual hardware: We measured open-circuit voltage before dispatch and confirmed the BMS-free primary cell construction delivers stable output with no internal protection circuit to trip under low-drain standby conditions.
  • Hot-swap procedure — critical: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off will erase SRAM contents immediately — there is no grace period. If the PLC was off during the swap, a full program reload from your programming device is required before restarting.

PLC battery alarm not clearing after a confirmed good installation

Most PLCs do not auto-clear a battery alarm when the cell is replaced — the alarm flag is latched in the controller's diagnostic register and requires a manual reset through your programming software. On Allen-Bradley platforms, this is done via the fault reset routine in Studio 5000 or RSLogix. On Siemens S7 controllers, clear the alarm in STEP 7 or TIA Portal under the hardware diagnostics menu. Failing to reset the flag will leave the alarm active even with a fully charged new cell installed.

New ER17/33 cell reading below 3.6V on first installation

Li-SOCl2 cells ship in a passivation state — a thin lithium chloride layer forms on the anode surface during storage and suppresses the open-circuit voltage temporarily. Once the cell is installed on the PLC's float circuit and draws its microamp standby current, the passivation layer breaks down and the voltage rises to the rated 3.6V within a few hours. No action is needed if the initial reading is between 3.2V and 3.5V. If the cell reads below 3.0V after 24 hours on the controller, replace it.

Compatible Models

ER17/33

Replaces Part Numbers

ER17/33

Technical Specifications

Voltage3.6V
Amp Hours1600mAh
Capacity1600mAh
Rate5.76Wh
Net Weight12.4g /0.44 oz
Gross Weight37.4g /1.32 oz
Approximate Weight37.4g /1.32 oz
Dimension 35.95 x 22.42 x 16.40mm

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 lost its program after I swapped the ER17/33 battery — what happened?

The SRAM holding the program has no backup path once the battery is removed and the controller is powered off — both power sources are gone simultaneously and memory is lost instantly. The ER17/33 must be swapped with the PLC powered on and in RUN mode so the SRAM stays live throughout the exchange. With memory gone, a full program reload from your programming device is the only fix. Connect your laptop, open the project file, and download the program to the controller before attempting a restart.

My PLC's real-time clock is showing the wrong date and time after replacing the battery — is the new cell faulty?

The RTC lost its register contents during the swap, which means it reset to a default or epoch date — this is expected if the controller was off at any point during the battery exchange. The cell itself is not faulty; the clock simply needs to be set again manually. Access the RTC configuration in your programming software — in TIA Portal this is under "Set time of day," and in RSLogix 5000 it is under the controller properties clock tab. Set the correct date and time, then write it to the controller.

The ER17/33 cells in our PLCs are depleting faster than the rated service life — we're replacing them every year instead of every three to five years.

Elevated enclosure temperature is the primary cause — Li-SOCl2 self-discharge roughly doubles for every 10°C rise above 25°C, so a cabinet running at 45°C can cut the service life by 75% or more. Check the ambient temperature inside the control panel with a thermocouple; if it exceeds 35°C consistently, improve cabinet ventilation or relocate heat-generating components away from the controller. Also confirm the controller is not drawing continuous milliamp-level current from the battery terminal due to a firmware fault — standby draw should measure below 100µA on a healthy system.

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