BCI MCR-1821J/1-H Capnocheck II Compatible Battery 7.4V 3400mAh

BCI Capnocheck II Capnograph Pulse Oximeter — 7.4V Li-ion Replacement Battery (MCR-1821J/1-H)

This 7.4V 3400mAh Li-ion battery replaces the OEM pack in the BCI Capnocheck II Capnograph Pulse Oximeter and compatible Capnocheck 8400 and 8401 units. It supports simultaneous end-tidal CO₂ and SpO₂ monitoring during patient assessments and transport. Voltage and capacity match OEM specifications to satisfy the device's BMS handshake on startup.

• Capnocheck II, 8400, and 8401 compatibility: These models share the same 7.4V battery rail, connector pinout, and BMS communication protocol. A single pack services the full range without any adapter or modification.
• Bench tested on actual hardware: We cycled this pack on a Capnocheck II under simultaneous capnography and oximetry load. The BMS completed its initialisation handshake, accepted the charge IC communication, and passed the device's internal self-test without triggering a battery fault code.
• Post-swap startup protocol: After installing this battery, allow the Capnocheck to complete its full power-on self-test cycle without interruption. The BMS runs a verification sequence at startup — cutting power during this window forces a false battery fault that persists until a clean reboot clears it.

Why the Capnocheck II alarms low battery immediately after a confirmed full charge

The Capnocheck II's charge IC applies a conservative current limit to cells it has not yet profiled. On the first charge cycle, the BMS may not register the pack as fully qualified, so the device flags a low-battery condition even when the cell is at full voltage. This is not a fault in the replacement pack — it is the BMS running a learn cycle. Complete one full charge-to-discharge-to-charge cycle, and the alarm clears. After that cycle, the device should recognise the pack and report charge level accurately.

Device will not power on after the battery sat in storage

Li-ion cells self-discharge at roughly 1–3% per month. A pack that shipped or stored for several months can drop below the BMS recovery threshold — typically around 2.5V per cell — and the device will show no response at all when the power button is pressed. The BMS enters a protection state at that voltage and blocks the discharge path entirely. Connect the battery to the OEM charger and leave it for a minimum of two hours before attempting to power on the device; most BMS circuits allow a slow recovery charge from as low as 2.0V per cell before re-enabling the output.