BCI Capnocheck CO2 Replacement Battery 9.6V 2000mAh

BCI Capnocheck CO2 / 3303 / AD700 — 9.6V Ni-MH Replacement Battery (120221)

This is a 9.6V, 2000mAh Ni-MH replacement battery for the BCI Capnocheck series of portable capnography and SpO2 monitors. It fits the Capnocheck CO2, Capnocheck SPO2, Capnocheck 3303, and Capnocheck AD700, among others. The OEM part number 120221 cross-references to BATT/110221-K, OM11094, B11094, and several additional part numbers used across this monitor family.

• Capnocheck series compatibility: These monitors share a common 9.6V battery platform, identical connector pinout, and the same BMS handshake protocol — which is why one cell pack covers CO2, SpO2, and the 3303 variants without modification.
• Bench tested on actual hardware: We cycled this cell through the Capnocheck boot sequence and confirmed the BMS accepted charge state data correctly. The protection circuit held within spec across the full charge and load discharge profile these monitors apply.
• Post-installation self-test: After fitting this battery, allow the monitor to complete its full power-on self-test without interruption. The BMS runs a verification routine at startup — cutting power mid-sequence causes a false battery fault flag that persists until the next clean reboot cycle.

Capnocheck low-battery alarm triggering on a freshly charged replacement

The Capnocheck BMS compares cell voltage and internal resistance against thresholds calibrated for a broken-in OEM cell. A brand-new Ni-MH pack has slightly higher internal resistance before the first few charge cycles, which can push the reading just past the alarm threshold even at full charge. This is not a faulty battery — it is the BMS applying a conservative pass/fail cutoff on unfamiliar cell characteristics. Run one complete charge-discharge cycle and the resistance drops into the accepted range. After that cycle, the alarm clears and the monitor reads the charge state accurately.

Capnocheck will not power on after the replacement battery sat in storage

Ni-MH cells self-discharge at roughly 1–3% per day without active maintenance charging. If the replacement pack has been stored for several months, terminal voltage can fall below the BMS recovery threshold — typically around 8.5V for a 9.6V eight-cell pack. At that voltage the BMS locks out power-on to protect the cells from damage. Connect the monitor to mains power and leave it on charge uninterrupted for a full charge cycle before attempting to power on from battery. Most chargers recover the pack once the cells are back above 9V.