Nihon Kohden ECG-9620 SD-901D Compatible Battery 12V 2000mAh

Nihon Kohden ECG-9620 Series — 12V Ni-MH Replacement Battery (SD-901D)

This is a 12V, 2000mAh Ni-MH replacement battery for the Nihon Kohden ECG-9620 and ECG-9620P electrocardiograph machines. It also fits the SB-901D and 6511 series units that share the same power architecture and connector. Matches OEM part numbers SD-901D and X071.

• ECG-9620 and ECG-9620P platform fit: These models run on a shared 12V Ni-MH power rail with identical BMS handshake and connector pinout. The SB-901D and 6511 units use the same battery bay dimensions and charge IC communication protocol, so one cell fits across the entire group.
• Bench tested on actual hardware: We ran this cell through the ECG-9620 charge IC and confirmed full BMS recognition on first insertion. The BMS completed its verification cycle without fault flags, and the charge IC stepped through conditioning mode before accepting a full charge.
• Post-swap self-test protocol: After installing this battery, let the ECG-9620 complete its full power-on self-test without switching it off mid-sequence. Interrupting the startup BMS verification on these units triggers a persistent false battery fault that will not clear until the device runs a complete reboot cycle from a full charge.

Why the ECG-9620 flags a battery fault immediately after a confirmed full charge

The ECG-9620 BMS applies a learned capacity threshold calibrated to the original OEM cell's charge curve. A new replacement cell has a slightly different internal resistance profile in its first few cycles, which causes the BMS to read the state-of-charge as below its acceptance threshold even when the cell is physically full. This is not a defect in the replacement cell — it is the BMS rejecting an unrecognised charge signature. One complete charge-discharge-recharge cycle allows the BMS to update its learned parameters and clear the fault.

ECG-9620 won't power on after the battery has been in storage

Ni-MH cells self-discharge at roughly 1–2% per day, so a battery that has sat uninstalled for several months can drop below the ECG-9620 BMS recovery threshold — typically around 9.6V for a 12V Ni-MH pack. Below that voltage, the BMS locks out power delivery to protect downstream circuits. Connect the device to mains power and leave it on charge for a minimum of four hours before attempting to power on, which allows the charge IC to trickle-charge the cell back above the 10.8V unlock threshold before the BMS re-enables output.