Fresenius MCM500 Replacement Battery 6V 3000mAh

Fresenius MCM500 Series — 6V Ni-MH Replacement Battery (120050)

This is a 6V, 3000mAh Ni-MH replacement battery for the Fresenius MCM500 and MCM500D volumetric infusion pumps. It matches OEM part numbers 120050 and BATT/110050. The battery supports portable operation when the pump is disconnected from AC power in hospital and clinical environments.

• MCM500 and MCM500D compatibility: Both models share the same 6V power rail, connector pinout, and BMS handshake protocol. A single cell format — 112.00 × 44.20 × 22.70mm — fits both variants without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge on the MCM500 platform. The BMS accepted the cell on first insertion, completed its verification cycle, and reported charge status accurately across the full capacity range.
• Post-installation self-test protocol: After fitting this battery, allow the pump to complete its full power-on self-test without interruption. The MCM500 runs a BMS verification sequence at startup — cutting power during this window creates a false battery fault flag that persists until the next clean reboot.

MCM500 low-battery alarm triggering on a freshly charged replacement

The MCM500's BMS applies a charge acceptance threshold calibrated to a conditioned cell. A new Ni-MH cell has not yet established its full electrochemical capacity profile, so the BMS reads available charge conservatively. This causes the pump to alarm low battery even when the cell is fully charged. One complete charge-discharge cycle allows the BMS to recalibrate its thresholds to the actual cell capacity. Run this conditioning cycle before placing the battery in clinical rotation.

Pump will not power on after the replacement cell sat in storage

Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A cell stored for several months can drop below the BMS recovery threshold — typically around 4.8V for a 6V pack — causing the pump to refuse to boot entirely. Connect the pump to AC power first and allow a trickle pre-charge for at least 30 minutes before attempting a standalone boot. Once the cell climbs above the BMS recovery floor, the pump will initialise normally and continue charging to full capacity.