Testo 350K Analyzer 11.1V Replacement Battery 0515 0039

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

This 11.1V 5200mAh (57.72Wh) Li-ion pack replaces the OEM battery in the Testo 350K and 350 GAS Analyzer. Both instruments are portable combustion and emissions analyzers used for flue gas measurement in HVAC and industrial survey work. The pack slots into the instrument's battery bay and connects through the same BMS communication interface as the original.

• 350K and 350 GAS compatibility: Both models run the same 11.1V three-cell architecture and share the OEM part number 0515 0039. The battery connector pinout and BMS handshake protocol are identical across both units, so one pack covers either instrument without modification.
• Bench tested on actual hardware: We cycled this pack through the 350K's probe initialisation sequence, which draws a short current spike as the electrochemical sensors power up. The BMS held the rail without tripping into protection mode, and cell voltage recovered cleanly between measurement cycles.
• Pre-deployment calibration cycle: After installing a fresh pack, run a full calibration cycle through the instrument's menu before heading to site. The 350K maps battery state during calibration — skipping this causes the instrument to flag premature low-battery warnings during the first measurement session in the field.

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

Li-ion cells self-discharge over time, and if the pack drops below roughly 2.5V per cell during storage, the BMS trips into deep-discharge protection and the instrument will not power on at all. The charger may also show no charge activity because it reads the pack as unrecoverable. Most chargers with a recovery or boost mode can push a small current into the pack to lift cell voltage above the BMS re-enable threshold. Connect the battery to the charger for at least 30 minutes — if cell voltage climbs above 9V total, normal charge will resume automatically.

Readings resetting or logging gaps during a sustained measurement session

When all sensor channels are active simultaneously during a long flue gas survey, the combined draw from the electrochemical cells, pump motor, and display creates a sustained load the aged OEM pack can no longer support cleanly. Voltage sags under this load, and the instrument interprets a brief undervoltage event as a power fault — resetting the active log or dropping data points. This is not a firmware issue; it is a capacity problem. A fresh pack at 5200mAh holds the voltage rail flat across the full sensor load without dropout.