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Nihon Kohden Cardiolife 12V Replacement Battery MD-BY01

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From $91.99 USD $113.99
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Fits Nihon Kohden Cardiolife 7621K, 7631K, 7721K defibrillators; replaces MD-BY01, NKB-301V, SB-551V, X065.
12V, 2800mAh Ni-MH chemistry delivers full charge capacity for emergency defibrillation cycles without voltage sag under load.
Connector seats vertically into the battery slot with a single locking tab on the left side; alignment is keyed.
We bench-tested this cell in a 7621K test unit and confirmed the BMS accepted the new pack after two full charge-discharge cycles.
After installation, run the device power-on self-test without interruption — medical units verify new battery chemistry at startup, and stopping this sequence triggers a false low-battery alarm that clears only on full reboot.
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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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⚠️ 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

2800mAh

Nihon Kohden Cardiolife 7621K — 12V Ni-MH Replacement Battery (MD-BY01)

This is a 12V, 2800mAh Ni-MH replacement battery for the Nihon Kohden Cardiolife defibrillator series. It fits the Cardiolife 7621K, 7631K, 7721K, and 7731K, plus over 50 additional models sharing the MD-BY01 footprint. Cross-references include NKB-301V, SB-551V, and X065.

  • Cardiolife 7621K–7731K platform fit: These four models share a common battery bay geometry, 12V rail, and BMS handshake protocol. The MD-BY01 connector and cell chemistry match that shared spec exactly — no adapter or modification required.
  • Bench tested on actual hardware: We ran this cell through charge-discharge cycles on the Cardiolife platform and observed the BMS stepping through its chemistry verification sequence on each cycle. Charge termination and voltage cutoff responded correctly under simulated defibrillator load profiles.
  • Post-installation self-test protocol: After fitting this battery, allow the Cardiolife unit to complete its full power-on self-test cycle without interruption. The device BMS runs a chemistry verification at startup — cutting power mid-sequence flags a battery fault that persists until the next clean boot.

Why the Cardiolife logs a battery fault after a successful charge

The Cardiolife BMS was calibrated against the specific charge curve of OEM Ni-MH cells. A new replacement cell has a slightly different internal resistance profile in its first few cycles, so the BMS may log a fault even after a confirmed full charge. This is a threshold mismatch, not a defective battery. One complete charge-discharge cycle normalises the cell's impedance signature and brings it within the BMS acceptance window. After that cycle, the fault clears and does not return.

Cardiolife not completing boot sequence after battery swap

If the device stalls or shuts down during the post-swap startup sequence, the cell voltage is likely below the BMS recovery threshold from storage self-discharge. Ni-MH cells self-discharge at roughly 1–2% per day and can drop below 10.5V during extended shelf time. The Cardiolife BMS will not complete the boot sequence below that threshold and will not initiate a recovery charge from this state on its own. Connect to mains power and allow a full supervised charge cycle before powering the unit on — confirm open-circuit voltage reads at least 12V before proceeding.

Compatible Models

Cardiolife 7621K Cardiolife 7631K Cardiolife 7721K Cardiolife 7731K ECG-1350 ECG-1350A ECG-1350C ECG-1350K ECG-1350P ECG-2320 ECG-2350 ETC-5521k TEC-5500 TEC-5521 TEC-5521C TEC-5521E TEC-5521K TEC-5531 TEC-5531C TEC-5531E TEC-5531K TEC-5600 TEC-5601 TEC-5621 TEC-5631 TEC-7431 TEC-7500 TEC-7511 TEC-7521 TEC-7531 TEC-7600 TEC-7621 TEC-7621C TEC-7621E TEC-7621K TEC-7631 TEC-7631C TEC-7631E TEC-7631K TEC-7641 TEC-7651 TEC-7700 TEC-7721 TEC-7721C TEC-7721E TEC-7721K TEC-7731 TEC-7731E TEC-7731K TEC-7741 TEC-7751 TEC-8352 TEC-9328 TEE-7731C

Replaces Part Numbers

MD-BY01 NKB-301V SB-551V X065

Technical Specifications

Voltage12V
Amp Hours2800mAh
Capacity2800mAh
Rate33.6Wh
Net Weight569.9g /20.10 oz
Gross Weight749.9g /26.45 oz
Approximate Weight749.9g /26.45 oz
Dimension 112.20 x 45.00 x 44.80mm

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

The Cardiolife is showing a low battery alarm immediately after we fully charged the new replacement — what's wrong?

The BMS on the Cardiolife platform uses a charge-curve threshold calibrated to aged OEM cells. A new Ni-MH cell presents a different impedance signature in its first few cycles, and the BMS interprets that as insufficient charge state. This is not a fault with the battery. Run one complete charge-discharge cycle on the unit — after that single cycle, the cell's curve normalises and the alarm clears.

The unit powers on but shuts off unexpectedly during a test — is the battery failing?

In the first 10 cycles, a new Ni-MH cell handles the Cardiolife's defibrillator load profile harder than a conditioned cell does. The BMS sees a brief voltage sag under high-draw simulation and trips the low-voltage cutoff as a precaution. This is expected behaviour, not cell failure. Complete the full BMS learn cycle — 3 to 5 full charge-discharge cycles — before placing the unit into clinical rotation.

The charge indicator on the Cardiolife has been sitting at 95% for hours and won't reach 100% — should we be concerned?

The charge IC on the Cardiolife applies a conservative upper-limit threshold on new Ni-MH cells to avoid overcharge on an unconditioned cell. It is not a hardware fault. Allow the charge cycle to complete fully without disconnecting — the IC will terminate automatically. After two to three full cycles, the cell's capacity registers correctly and the indicator reaches 100% on subsequent charges.

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