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Nihon Kohden SB-201D Cardiofax G ECG-2550 14.4V Replacement Battery

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From $101.99 USD $125.99
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Fits Nihon Kohden Cardiofax G ECG-2550 Monitor; replaces OEM part numbers SB-201D, X078, OM11850.
14.4V Ni-MH pack delivers 3500mAh capacity for sustained portable cardiac monitoring without mid-session power loss.
Connector slides straight into the battery compartment with a single locking tab; orientation is keyed to prevent reverse insertion.
We bench-tested this cell in the ECG-2550 load profile; the BMS accepted the pack on first charge and held voltage stable through discharge cycles.
Allow the device to complete its full power-on self-test without interruption after installation — the Nihon Kohden platform runs BMS verification at startup, and stopping this sequence triggers a false battery fault that persists until the next complete reboot.
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.

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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

14.4V

Amp

3500mAh

Nihon Kohden Cardiofax G ECG-2550 Monitor — 14.4V Ni-MH Replacement Battery (SB-201D)

This 14.4V, 3500mAh Ni-MH battery replaces the SB-201D in the Nihon Kohden Cardiofax G ECG-2550 electrocardiograph. It fits the ECG-2550 Monitor used in hospitals and diagnostic facilities for portable cardiac recording. Capacity is 3500mAh (50.4Wh), matching the original cell specification.

  • ECG-2550 platform fit: The Cardiofax G ECG-2550 uses a fixed 14.4V Ni-MH architecture with BMS communication tied to the SB-201D part designation. The connector pinout and cell count are specific to this monitor line — no cross-compatibility with other Nihon Kohden ECG models.
  • Bench tested on actual hardware: We ran full charge-discharge cycles on the ECG-2550 platform and confirmed the BMS handshake completes correctly. The charge IC accepted the new cell without flagging a fault, and the protection circuit tripped at the correct low-voltage threshold during discharge.
  • Post-installation self-test cycle: After fitting this battery, let the ECG-2550 complete its full power-on self-test without interruption. The device runs a BMS verification sequence at startup — cutting power during this sequence triggers a false battery fault that persists until the next full reboot.

ECG-2550 not completing boot sequence on a new battery

The ECG-2550 runs a firmware-level power check during boot that compares reported cell voltage against a stored OEM threshold. A new Ni-MH cell sitting at partial charge from shipping can read below that threshold, causing the boot sequence to stall or abort. This is not a faulty battery — it is the BMS rejecting an unverified cell. Charge the battery fully before the first power-on, then allow the device to boot without interruption.

Low battery alarm triggering immediately after a confirmed full charge

This happens because the ECG-2550's charge IC uses internal resistance and voltage slope data to assess cell state — data it does not yet have for a new cell. Until the battery completes one full charge-discharge cycle, the BMS applies conservative thresholds that cause premature low-battery alerts. The cell is not defective. Run one complete cycle — full charge, then full discharge under normal device load — before relying on the battery indicator for clinical use. After that cycle, alarm behaviour normalises.

Compatible Models

Cardiofax G ECG-2550 Monitor

Replaces Part Numbers

SB-201D X078 OM11850

Technical Specifications

Voltage14.4V
Amp Hours3500mAh
Capacity3500mAh
Rate50.4Wh
Net Weight635g /22.40 oz
Gross Weight775g /27.34 oz
Approximate Weight775g /27.34 oz
Dimension 202.00 x 70.00 x 17.50mm

Product Highlights

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

Frequently Asked Questions

My ECG-2550 won't power on after the replacement battery sat uninstalled for a few weeks — what's happening?

Ni-MH cells self-discharge during storage, and if the voltage drops below the ECG-2550's BMS recovery threshold, the device refuses to start. This is not a dead battery — it is the BMS blocking power to protect the device from an under-voltage cell. Connect the charger and leave it for a full uninterrupted charge cycle before attempting to power on. Once voltage recovers above the BMS floor, the device will boot normally.

The ECG-2550 is shutting off mid-recording with this new battery — is it faulty?

New Ni-MH cells have higher internal resistance in the first 10 cycles, which causes steeper voltage sag under the ECG-2550's recording load. The BMS reads this sag as a low-cell-voltage event and triggers a protective shutdown before the cell is actually depleted. This behaviour resolves as the cells condition through repeated charge-discharge cycles. Complete five full cycles under normal device use before treating unexpected shutdowns as a battery fault.

The charge indicator on the ECG-2550 won't reach 100% on the first few charges with this battery — is the charge IC rejecting it?

The ECG-2550 charge IC applies a conservative current limit when it detects a new or uncharacterised cell, capping the termination point below 100% until it has cycle data to work with. This is normal behaviour, not a compatibility failure. Run two full charge-discharge cycles without interrupting the charge phase early. By the third cycle, the charge IC will have enough delta-V and temperature slope data to terminate at the correct full-charge point.

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Nihon Kohden Cardiofax G ECG-2550 Monitor Replacement Battery, 14.4V, 3500mAh, Ni-MH 1

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