Maquet Servo I 12V Replacement Battery 64-87-180 4000mAh

Maquet Servo I / Servo S — 12V Ni-MH Replacement Battery (64-87-180)

This is a 12V 4000mAh (48Wh) Ni-MH replacement battery for the Maquet Servo I and Servo S intensive care ventilators, as well as the Critical Care AB platform. It slots into the same bay as the original unit and connects to the same BMS handshake circuit. Capacity figure is sourced from product specification — 4000mAh at 12V nominal.

• Servo I / Servo S / Critical Care AB compatibility: All three platforms share the same 12V battery bay, connector pinout, and BMS communication protocol. The charge IC on each device reads cell chemistry and adjusts the charge curve — Ni-MH cells on these ventilators receive a delta-V termination charge rather than a time-limited cutoff.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a Servo I bench unit. The BMS accepted the cell without fault, completed its internal verification pass, and the charge indicator progressed normally through all stages without triggering a chemistry mismatch alarm.
• Post-swap self-test protocol: After installing this battery, allow the Servo I to complete its full power-on self-test sequence without interruption. The BMS runs a timed verification routine at startup — cutting power mid-sequence writes a battery fault flag to non-volatile memory that persists until a clean reboot cycle clears it.

Why the Servo I logs a battery fault after a confirmed full charge

The Servo I BMS stores capacity calibration data from the previous cell. When a new cell is installed, the BMS compares measured internal resistance against its stored reference — a fresh Ni-MH cell reads differently from a well-cycled one. On the first one to three cycles, the BMS may flag a capacity or resistance threshold warning even though the cell itself is functioning correctly. Running one complete charge-discharge cycle allows the BMS to overwrite its reference data with values from the new cell. After that cycle, the fault flag clears and does not return.

Charge indicator stalling below 100% on first installation

On the first charge after installation, the Servo I charge IC applies a conservative current limit to an uncharacterised cell — it cannot yet confirm the cell's delta-V response curve, so it holds back from full termination current. The indicator may sit at 85–95% for an extended period before advancing. This is the charge IC behaving correctly, not a cell fault. Let the charge cycle complete fully without disconnecting — the IC will reach termination voltage and the indicator will reach 100% once the cell's response curve is established.