Air Liquide Monnal T50 Replacement Battery 21.6V 4400mAh

Air Liquide Monnal T50 — 21.6V Li-ion Replacement Battery (YR109301031404)

This 21.6V 4400mAh Li-ion battery replaces the OEM pack in the Air Liquide Monnal T50 portable mechanical ventilator. It fits the MT50 and MT50-04888 variants and delivers 95.04Wh of capacity to sustain ventilation during patient transport or when mains power is unavailable. Voltage, connector, and BMS communication protocol match the original Air Liquide specification.

• Monnal T50 / MT50 platform fit: The MT50, MT50-04888, and Monnal T50 all share the same 21.6V battery bay, connector pinout, and BMS handshake. One replacement pack covers all three variants without modification.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the Monnal T50 platform. The BMS authenticated correctly, charge termination triggered at the expected voltage ceiling, and the device reported battery status without fault codes across repeated power cycles.
• Post-swap self-test protocol: After installing this battery, allow the Monnal T50 to complete its full power-on self-test without interruption. The device runs a BMS verification sequence at startup — cutting power mid-sequence causes the ventilator to log a battery fault that persists until the next clean reboot.

Monnal T50 low battery alarm triggering immediately after a confirmed full charge

The Monnal T50's BMS compares incoming cell data against stored thresholds calibrated for an OEM-aged cell profile. A new cell with a slightly different initial internal resistance reading can fall outside that threshold on the first cycle, triggering a low battery alarm even at full charge. This is not a cell fault — it is the BMS learn cycle running against an unfamiliar chemistry signature. Run one complete charge-to-discharge-to-full-charge cycle before clinical deployment. After that cycle, the BMS recalibrates its reference values and the alarm clears.

Monnal T50 failing to complete boot sequence after battery swap

If the ventilator stalls mid-boot after a battery replacement, the most common cause is the cell voltage sitting below the BMS boot-enable threshold — typically around 19.8V — after a period of storage-related self-discharge. Li-ion cells self-discharge at roughly 2–3% per month, and a pack that has sat in warehouse stock can drop low enough that the device halts the boot sequence as a protective measure. Connect the ventilator to mains power and allow the battery to pre-charge for at least 30 minutes before attempting to boot on battery alone. Once cell voltage climbs above 20.5V, the boot sequence completes normally.