Testo 350K Analyzer 11.1V Replacement Battery 0515 0039

Testo 350K Analyzer — 11.1V Li-ion Replacement Battery (0515 0039)

This 11.1V, 6800mAh Li-ion pack replaces the OEM battery in the Testo 350K and 350 GAS Analyzers. Both are combustion flue gas analyzers used by HVAC technicians to measure exhaust emissions and heating system efficiency in the field. Voltage and capacity match the original specification exactly.

• 350K and 350 GAS compatibility: Both analyzers share the same battery bay, connector pinout, and BMS communication protocol. The 0515 0039 part number covers both units — the internal cell configuration, protection circuit, and thermistor line are identical across the pair.
• Bench tested on actual hardware: We ran this pack through a full charge cycle and monitored the BMS handshake at power-on. The protection circuit responded correctly to the analyzer's sensor initialisation current spike, and the charge controller accepted the pack without fault codes.
• Post-install calibration on the 350K: After fitting this battery, run a full calibration cycle through the instrument menu before heading to site. The 350K maps battery state during calibration — skipping this step causes premature low-battery warnings during the first measurement session, even with a fully charged pack.

BMS lockout after the 350K sat unused in a carry case for months

Li-ion cells left in storage self-discharge slowly. If the pack drops below roughly 2.5V per cell — around 7.5V total — the BMS trips into deep-discharge lockout and will not respond to the charger or the instrument. This is a protection state, not a dead pack. To recover it, connect the original Testo charger and leave it for up to 30 minutes before the BMS re-initialises and allows normal charging to begin. If the charger LED never shifts from fault to charge, the cells have gone below recovery threshold and the pack will need replacing.

350K shuts down mid-measurement when the heated probe initialises

The 350K's heated probe draws a sharp current spike at initialisation — this is normal behaviour, but an aged or partially discharged OEM pack can trigger the BMS overcurrent cutoff at that moment. The analyzer shuts off without warning, even when the battery indicator showed adequate charge. This replacement pack carries a higher cell capacity at 6800mAh, which lowers internal resistance and keeps voltage stable through the probe start-up surge. Charge the pack fully before the first field session to ensure the BMS enters the measurement session at rated headroom.