Honeywell XT-BAT-K1 BW Max XT II Replacement Battery 3.7V 3000mAh

Honeywell BW Max XT II — 3.7V Li-Polymer Replacement Battery (XT-BAT-K1)

This 3.7V, 3000mAh lithium-polymer battery replaces the OEM pack in the Honeywell BW Max XT II and BW GasAlert Max XT II portable multi-gas detectors. It also fits the GasAlert Max XT Legacy Multigas Monitor and the Max XT II multi-gas detector series. Part number XT-BAT-K1 matches the original connector, BMS handshake, and housing dimensions exactly.

• BW Max XT II platform fit: All listed Max XT II variants share the same 3.7V power rail, the same polarised connector, and the same BMS communication protocol. The detector's firmware validates the pack at startup — this battery passes that check on the BW Max XT II and BW GasAlert Max XT II without triggering a battery fault flag.
• Bench tested on actual hardware: We ran this pack on a BW Max XT II unit and logged the BMS response across the sensor initialisation spike and sustained four-sensor load. The protection circuit held within spec at both draw peaks, and the pack completed a full charge cycle without thermal trip.
• Post-install calibration requirement: After fitting this battery, run a full sensor calibration cycle through the instrument menu before field deployment. The Max XT II maps battery state during calibration — skipping this step causes the detector to display premature low-battery warnings on the first monitoring session.

BMS lockout on the Max XT II after the pack sat unused for months

Lithium-polymer cells in low-draw instruments self-discharge slowly over storage. If the BW Max XT II sat unused long enough, the cell voltage can drop below 3.0V — the threshold where the BMS locks out to prevent cell damage. At that point the detector shows no signs of life and the charger may not initiate a charge cycle at all. Connecting the unit to the OEM charger for 15–20 minutes without interruption usually wakes the BMS via a trickle pre-charge mode. If the pack recovers, the open-circuit voltage should read above 3.4V before the main charge cycle kicks in.

Max XT II shuts down mid-survey with no prior low-battery warning

This happens when the pack's resting voltage reads acceptable but sags sharply under the combined draw of all four sensors running simultaneously. The BMS interprets the voltage sag as a critically low cell and triggers a protection cutoff — the detector shuts off without cycling through the normal low-battery alarm sequence. An aged or partially depleted cell causes this even when the on-screen indicator shows 30–40% remaining. Charge the pack to full, allow it to rest for ten minutes, then check that the open-circuit voltage holds above 3.7V before redeploying.