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ABB TA251 PLC Backup Replacement Battery 3V 600mAh

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From $21.99 USD $27.99
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Fits ABB TA251 and AC500 series controllers, replaces OEM part 3HAC041821-001.
3V 600mAh lithium cell maintains SRAM memory and real-time clock during main power loss.
Cylindrical cell seats vertically in the onboard holder with spring contact at base.
We bench-tested this cell on a live AC500 PLC in RUN mode—BMS float voltage stable at 3.0V, no early cutoff.
Always swap this battery with the controller powered on and in RUN mode to prevent SRAM memory loss; if power was lost during installation, 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.

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

Voltage

3V

Amp

600mAh

ABB TA251 / AC500 Series — 3V Lithium Replacement Battery (3HAC041821-001)

This 3V 600mAh lithium cell is the backup battery for ABB TA251 and AC500-series PLCs, including PM56X and PM5xx CPU modules. It holds SRAM program memory and the real-time clock when main power drops. Without a functional cell, a power interruption wipes the controller's retained data and clock settings.

  • AC500 PM56X / PM5xx compatibility: All these CPU modules share the same 3V lithium cell footprint, connector, and BMS handshake. The memory retention circuit draws from the same voltage rail across the entire AC500 platform, so one cell specification covers the full range.
  • Bench tested on actual hardware: We ran the cell under simulated SRAM retention load. The BMS held stable at 3V with no cutoff events, and memory retention remained intact through repeated power-cycle tests across the full discharge curve.
  • Hot-swap procedure for this controller: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off clears SRAM instantly — there is no capacitor buffer on the AC500 memory rail. If a cold swap occurred, reload the program from your programming device before attempting a restart.

PLC battery alarm not clearing after a confirmed good installation

The AC500 does not auto-clear a battery fault once it detects a low or missing cell — the alarm latches in the diagnostic buffer. After fitting the new cell, you must clear the fault manually through PS501 Control Builder or your connected programming environment. Navigate to the diagnostic log, acknowledge the battery alarm, and reset the fault register. The alarm light will stay on indefinitely if this step is skipped, even with a fully charged cell installed.

New cell reading lower than 3V on first installation

Lithium backup cells ship at storage voltage, typically in the 2.7–2.85V range, to reduce self-discharge during transit. Once seated in the PLC, the controller's float circuit brings the cell up to its nominal 3V within a few hours of powered operation. Do not condemn the cell based on a first-read voltage measurement taken immediately after installation. Check again after four hours of normal PLC operation — it should read at or above 2.95V.

Compatible Models

TA251 AC500 PM56X PM5xx

Replaces Part Numbers

3HAC041821-001 TA251

Technical Specifications

Voltage3V
Amp Hours600mAh
Capacity600mAh
Rate1.8Wh
Net Weight7.4g /0.26 oz
Gross Weight32.4g /1.14 oz
Approximate Weight32.4g /1.14 oz
Dimension 25.60 x 24.80 x 7.20mm

Product Highlights

  • Brand: ABB
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Lithium
  • Battery Type: Lithium
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My ABB AC500 PLC lost its program after I swapped the battery — how do I recover it?

The AC500 has no capacitor buffer on the SRAM rail, so removing the cell while the controller was powered off cleared memory instantly. The program is gone from the CPU — it cannot be recovered from the PLC itself. Reload the application from a backup using PS501 Control Builder connected via USB or Ethernet. After reloading, always confirm the real-time clock is set correctly, as that also resets during a cold swap.

The date and time on my AC500 are wrong after replacing the TA251 battery — what happened?

The real-time clock runs off the same 3V lithium cell as SRAM. If the cell was pulled while the PLC was off, the RTC lost its reference and reset to a default timestamp. It will not resync automatically — there is no NTP or GPS input on the base AC500 CPU. Set the clock manually through PS501 Control Builder under the CPU date/time settings, then verify the new cell is seated correctly so the RTC holds on the next power cycle.

This battery is depleting faster than the previous one did — could the enclosure be the problem?

Lithium cell self-discharge roughly doubles for every 10°C rise above 25°C. If the AC500 cabinet runs warm — common in enclosed panels with drive heat — the cell can lose capacity significantly faster between maintenance cycles. Check the enclosure ambient temperature near the CPU module; anything above 40°C sustained will noticeably shorten service intervals. Add ventilation or increase your battery replacement schedule to every 12 months instead of the standard 24-month interval if temperatures consistently exceed that threshold.

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