Biomedical ECG-1A Replacement Battery 12V 2000mAh Ni-MH

Biomedical ECG-1A / ECG-220 Series — 12V Ni-MH Replacement Battery (HYHB-1172)

This is a 12V, 2000mAh Ni-MH replacement battery for the Biomedical ECG-1A, ECG-2201, ECG-2201G, and ECG-220 portable electrocardiograph monitors. OEM part number HYHB-1172. It fits the original battery bay and connects to the same BMS interface the monitor expects at startup.

• ECG-1A and ECG-220 series compatibility: These four models share the same 12V power rail, connector pinout, and BMS handshake protocol — one cell format covers the full range. Voltage tolerance across the series is tight, and all four reject cells that fall outside the OEM threshold during self-test.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on the ECG platform. The BMS accepted the cell on first handshake, completed its verification sequence without fault flags, and held voltage within spec across the discharge curve.
• Power-on self-test sequence: After installing this battery, let the monitor run its full startup self-test without interruption. The ECG-220 series runs BMS verification during boot — cutting power mid-sequence triggers a latching battery fault that persists until the next clean reboot cycle.

Why the ECG-220 series rejects a new cell during startup self-test

The ECG-220 BMS checks cell voltage and internal resistance at boot against thresholds calibrated to a conditioned OEM cell. A fresh Ni-MH cell straight from storage has higher internal resistance than a cycled one. If the monitor runs self-test before the cell has completed at least one full charge-discharge cycle, the resistance reading can trip the battery fault threshold. This is not a defective cell — it clears after one conditioning cycle. Run a full charge, then a full discharge under normal use, before relying on the monitor in a clinical setting.

Charge indicator stalls before 100% on the first charge

The ECG platform's charge IC applies a conservative current limit when it sees a new Ni-MH cell with an unfamiliar resistance profile. This can cause the charge indicator to plateau at 85–95% and stop advancing. The cell is not faulty — the charge IC is holding back until the cell's resistance drops into its expected window. Remove the battery, let it rest for 15 minutes, then reinstall and restart the charge cycle. By the second or third charge, the IC recognises the cell's profile and allows the full charge current through to 100%.