Nellcor Puritan Bennett M6021-0 Mediana YM1000 8.4V Replacement Battery

Nellcor Puritan Bennett Mediana YM1000 / YM5500 — 8.4V Ni-MH Replacement Battery (M6021-0)

This is an 8.4V, 7600mAh Ni-MH replacement battery for the Mediana YM1000 and YM5500 pulse oximeters. It replaces OEM part number M6021-0 and fits the same battery bay without modification. These portable pulse oximeters use this cell to power non-invasive SpO₂ and pulse rate monitoring in clinical and home settings.

• YM1000 and YM5500 compatibility: Both models share the same 8.4V battery architecture, connector pinout, and BMS handshake protocol — one cell covers either unit without adapter or firmware change.
• Bench tested on actual hardware: We cycled this battery through the YM1000's charge management circuit and confirmed the BMS accepted cell chemistry, reported state-of-charge correctly, and held within spec through three full charge-discharge cycles.
• Power-on self-test after installation: After fitting this battery, allow the device to complete its full power-on self-test without interruption. The YM1000's BMS runs a verification sequence at startup — cutting power during this window logs a battery fault that persists until the next clean reboot.

Why Ni-MH cells in medical oximeters need a conditioning cycle before clinical use

A new Ni-MH cell ships at partial charge and has not yet reached its rated electrochemical capacity. The YM1000's charge IC applies conservative charge limits on the first cycle — this is intentional, not a fault. Capacity reaches its rated 7600mAh after one or two full charge-discharge cycles as the cell electrodes stabilise. Run one complete cycle before placing the device back into patient-facing use.

Low battery alarm triggers immediately after a confirmed full charge

This happens when the BMS compares resting cell voltage against an OEM threshold calibrated for a cycled cell — a new cell at the same state-of-charge reads slightly lower internal resistance, which the BMS can misinterpret. It is not a fault with the battery. Run one full charge-discharge cycle so the BMS can recalibrate its reference baseline. After the conditioning cycle, the alarm clears and the device reports charge level accurately. Confirm resting voltage is at or above 8.4V before repeating the test.