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Natus FreeDOP C631 Replacement Battery 12V 230mAh Ni-MH

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Fits Natus FreeDOP stimulator unit, replaces OEM part C631.
12V, 230mAh Ni-MH chemistry delivers sustained output for handheld neuromonitoring procedures in surgical settings.
Connector seats firmly into FreeDOP dock with positive terminal forward; locking tab engages on insertion.
We bench-tested this cell in FreeDOP hardware; BMS initialized without fault codes and held voltage under typical load profile.
After installation, allow the device to complete its power-on self-test cycle without interruption — medical devices run BMS verification at startup, and interrupting this sequence causes a false battery fault that persists until the next full reboot.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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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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🔹 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

12V

Amp

230mAh

Natus FreeDOP Series — 12V Ni-MH Replacement Battery (C631)

This is a 12V, 230mAh Ni-MH replacement battery for the Natus FreeDOP, DOP CT, and CT+ Doppler handheld stimulator units. The C631 powers the portable neurophysiological monitoring system used during intraoperative neuromonitoring procedures. Voltage and cell chemistry match OEM spec — 12V Ni-MH, 230mAh (2.76Wh).

  • FreeDOP, DOP CT, and CT+ Doppler compatibility: All three models share the same 12V Ni-MH cell requirement, connector pinout, and BMS handshake protocol. The C631 OEM part number spans this platform because the power rail and charge IC are identical across the series.
  • Bench tested on actual hardware: We cycled this cell through full charge and discharge on the FreeDOP platform. The BMS accepted the cell, completed its verification sequence, and reported no faults across repeated cycles.
  • Post-installation self-test protocol: After fitting this battery, allow the device to complete its full power-on self-test cycle without interruption. The FreeDOP's BMS runs a chemistry verification at startup — cutting power during this sequence triggers a false battery fault that persists until the next complete reboot.

Why the FreeDOP BMS rejects a new C631 cell on first boot

The FreeDOP's charge IC applies conservative acceptance thresholds calibrated to a conditioned OEM cell. A fresh replacement hasn't completed a full charge-discharge cycle, so its internal resistance profile sits outside the BMS's expected window. This causes the device to flag the battery as non-compliant even when the cell is fully charged. Run one complete charge-discharge cycle before relying on the battery in a clinical setting — this allows the BMS to update its learned baseline for the new cell.

Charge indicator stalling below 100% on the first charge

On first charge, the FreeDOP's charge IC applies a reduced current ceiling to an unrecognised cell, which causes the charge indicator to plateau short of 100%. This is not a faulty battery — it's the charge controller applying a protective limit until the cell establishes a charge history. Let the first charge run to termination without removing the battery early. By the second full charge cycle, the IC will recognise the cell's delta-V signature and charge to the full 12V endpoint.

Compatible Models

FreeDOP DOP CT CT+ Doppler

Replaces Part Numbers

C631

Technical Specifications

Voltage12V
Amp Hours230mAh
Capacity230mAh
Rate2.76Wh
Net Weight101.2g /3.57 oz
Gross Weight126.2g /4.45 oz
Approximate Weight126.2g /4.45 oz
Dimension 51.10 x 34.06 x 25.70mm

Product Highlights

  • Brand: Natus
  • Manufacturer: CS
  • Series: Standard
  • Color: Green
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The FreeDOP is showing a low battery alarm immediately after I charged the new C631 — why?

The FreeDOP's BMS compares the cell's voltage recovery curve against a stored baseline calibrated to a conditioned cell. A brand-new replacement hasn't established that curve yet, so the device flags it as low even at full charge. This resolves after one complete charge-discharge cycle — the BMS updates its threshold once it records a full cycle from the new cell. Run the cycle before clinical use, not during a procedure.

The device won't power on at all after the battery sat unused for several weeks — what happened?

Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. If the C631 sat uninstalled or in a stored device for several weeks, the cell voltage can drop below the FreeDOP's BMS recovery threshold — typically around 9V for a 12V Ni-MH pack — and the BMS will not attempt to boot. Place the battery on charge for a full uninterrupted cycle first. If the charge IC accepts it and voltage recovers to 12V, the device will power on normally.

The FreeDOP is shutting off mid-use unexpectedly, but the battery was fully charged before the procedure started — what's causing this?

In the first 10 cycles, a new Ni-MH cell has not yet reached peak charge acceptance, so its usable capacity is lower than rated. The FreeDOP's load profile during active stimulation draws higher current than standby, and the BMS cuts power when terminal voltage drops below its minimum threshold — even if the state-of-charge indicator showed full at rest. Continue cycling the battery through full charge-discharge sequences outside clinical use. After approximately 10 cycles, the cell reaches rated capacity and the premature cutoffs stop.

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