About this replacement
Fresenius Vial MCM440 PT — 6V Ni-MH Replacement Battery (120238)
This is a 6V 3000mAh Ni-MH replacement battery for the Fresenius Vial MCM440 PT infusion pump and compatible Fresenius Vial models. It matches OEM part numbers 120238 and RC3000SC05AA. The cell fits the Vial MCM440 OT, MCM550 ST, Optima VS, and seventeen additional Fresenius pump models sharing the same voltage rail and connector format.
- MCM440 and Optima series compatibility: These pumps share a common 6V battery bay, BMS handshake protocol, and connector pinout across the MCM440 PT, MCM440 OT, MCM550 ST, and Optima VS platforms — one cell services the full range without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Fresenius pump platform. The BMS accepted the cell, completed its verification handshake, and held voltage within the pump's operating window across the full discharge curve.
- Post-installation self-test procedure: After installing this battery, allow the pump to complete its full power-on self-test without interruption. Medical-grade BMS firmware runs a verification sequence at startup — cutting power during this window triggers a false battery fault that persists until the next complete reboot.
Low battery alarm triggering on a fully charged new cell
Fresenius infusion pumps apply a BMS threshold calibrated to a conditioned OEM cell. A brand-new Ni-MH cell has not yet stabilised its internal resistance, so the pump's BMS reads a slightly elevated resistance value and flags it as low charge. This is not a fault with the cell. Run one complete charge-discharge cycle on the pump before clinical use — after that first full cycle, the BMS recalibrates and the alarm clears. The pump should read a stable charge state at or above 6.0V resting voltage after cycle one.
Pump will not power on after battery has been in storage
Ni-MH cells self-discharge at roughly 1–2% per day in storage. If a replacement cell sat unused for several months, its voltage may have dropped below the pump's BMS recovery threshold — typically around 5.4V for a 6V Ni-MH pack. The BMS will refuse to boot the device rather than risk operating on a deeply discharged cell. Place the battery in a compatible Fresenius charger and run a full charge cycle before insertion. Once voltage recovers above the BMS recovery floor, the pump will power on normally.