Nonin AS35108 Capnocheck Plus Replacement Battery 6V 5000mAh

Nonin Capnocheck Plus / 9400 Series — 6V Ni-MH Replacement Battery (AS35108)

This is a 6V 5000mAh Ni-MH replacement battery for the Nonin Capnocheck Plus, 9400, and Sleep CO2 Monitor. These portable capnography monitors use this cell pack to power continuous end-tidal CO₂ measurement during clinical procedures. Capacity matches the OEM specification at 30Wh.

• Capnocheck Plus / 9400 / Sleep CO2 platform fit: All three models share the same 6V rail, AS35108 connector pinout, and BMS handshake protocol. The charge IC in each device is calibrated to the Ni-MH chemistry voltage curve, so the cell chemistry here must match — Li-ion substitutes will fail the internal self-test.
• Bench tested on actual hardware: We cycled this pack through full charge-discharge on the 9400 platform. The BMS accepted the cell on first insertion and completed the startup verification sequence without fault. Capacity delivery tracked within 3% of the 5000mAh rating by cycle two.
• Startup self-test protocol: After fitting this battery, allow the Capnocheck to complete its full power-on self-test without interruption. The device runs a BMS verification routine at boot. Cutting power mid-sequence logs a battery fault that persists until the next clean reboot — it is not a cell defect.

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

The Capnocheck's charge IC uses a delta-V termination curve tuned to the original OEM cell's internal resistance profile. A new replacement cell has a slightly different resistance signature during the first charge cycle, which can cause the IC to terminate early and report a partial charge. The BMS then reads the pack as below its low-battery threshold at startup. Run one full charge-discharge cycle before clinical deployment — by cycle two, the IC correctly maps the cell's voltage curve and the alarm clears.

Device not powering on after battery sat in storage

Ni-MH cells self-discharge at roughly 20–30% per month unprotected. If this pack has sat in a warehouse or drawer, cell voltage may have dropped below the Capnocheck's BMS recovery threshold — typically around 4.8V for a 6V pack. The BMS will refuse to boot rather than draw from a deeply discharged cell, which is a protection behaviour, not a fault. Place the battery in the device and connect to mains charge for a minimum of 15 minutes before attempting power-on; most BMS circuits re-initialise once cell voltage climbs back above 5.4V.