KARL STORZ C-MAC 8401ZX Replacement Battery 3.7V 4800mAh

KARL STORZ C-MAC 8401ZX Series — 3.7V Li-ion Replacement Battery (ET27-30-0003723)

This is a 3.7V, 4800mAh lithium-ion battery for the KARL STORZ C-MAC video laryngoscope system. It fits the C-MAC 8401ZX, 8402 ZX, and related Endoscopy C-MAC 8401ZX variants. OEM cross-references include ET27-30-0003723, 30.0003, MB467, and OM11806.

• C-MAC 8401ZX and 8402 ZX platform fit: These models share a common battery bay, connector pinout, and BMS handshake protocol. The same 3.7V cell architecture runs both the video stack and the LED illumination rail, so voltage tolerance across that shared bus is tight.
• Bench tested on actual hardware: We cycled this cell through the C-MAC boot sequence and monitored BMS communication. The battery authenticated correctly, completed the power-on self-test without fault flags, and held voltage under the device's combined imaging and light load.
• Post-swap startup protocol: After installing this battery, allow the C-MAC to complete its full power-on self-test cycle without interruption. The device runs a BMS verification routine at startup — cutting power during this sequence triggers a false battery fault that persists until the next clean reboot.

C-MAC low battery alarm firing on a freshly charged replacement

The C-MAC's BMS uses stored calibration data from the previous cell to set its low-battery threshold. A new cell's state-of-charge curve doesn't match that stored profile on the first cycle, so the device flags it as low even at full charge. This isn't a fault with the cell — it's the charge IC applying a conservative limit until the BMS completes a learn cycle. Run one full charge-to-discharge cycle outside of clinical use. After that cycle, the alarm threshold recalibrates to the new cell's actual voltage curve.

C-MAC failing to power on after the replacement battery sat in storage

Li-ion cells self-discharge during storage, and the C-MAC's BMS has a minimum recovery voltage below which it refuses to initialise — typically around 3.0V per cell. If the battery shipped or sat uninstalled for several weeks, it may have dropped below that threshold. Connect the battery to the charger for at least 30 minutes before inserting it into the device; the charger applies a trickle pre-charge that brings the cell above the BMS recovery floor. Once voltage climbs above approximately 3.2V, the device will power on normally.