Smiths Capnocheck II 7.4V 2600mAh Replacement Battery 8408

Smiths Capnocheck II Capnograph & Oximeter — 7.4V Li-ion Replacement Battery (8408)

This is a 7.4V, 2600mAh Li-ion battery for the Smiths Capnocheck II Capnograph and Oximeter. It replaces OEM part number 8408 and fits the same battery bay without modification. Voltage and cell chemistry match the original specification exactly.

• Capnocheck II platform compatibility: Both the Capnograph and Oximeter variants of the Capnocheck II share the same 7.4V battery rail, connector pinout, and BMS handshake protocol — a single cell fits either unit without adapter or firmware difference.
• Bench tested on actual hardware: We ran this cell through the Capnocheck II power-on sequence, confirmed the BMS handshake completed correctly, and verified the charge IC accepted a full charge cycle without fault codes.
• Post-swap self-test requirement: After installing this battery, allow the device to complete its full power-on self-test without interruption. The Capnocheck II runs a BMS verification step at startup — cutting power during this sequence triggers a battery fault flag that persists until the next clean reboot.

Device not completing boot sequence after battery swap

The Capnocheck II runs a multi-stage boot sequence that includes a BMS verification check before the main operating screen loads. A new cell that has not yet completed its first full charge-discharge cycle may sit at a resting voltage slightly outside the BMS's expected threshold window. This causes the device to stall mid-boot or display a battery fault rather than completing initialisation. Run one full charge cycle to 8.4V before the first clinical use — the BMS calibrates its state-of-charge model on that first cycle.

Low battery alarm triggers immediately after a confirmed full charge

This alarm pattern is common on the first two or three cycles with a new cell. The Capnocheck II's charge indicator and low-battery threshold are tuned to the capacity curve of a conditioned OEM cell — a new replacement cell has a slightly different internal resistance profile until it has been cycled. The BMS interprets this as a capacity shortfall and fires the alarm early. Complete one full charge and one full discharge under normal device use, and the alarm threshold recalibrates to the new cell's actual curve.