Testo 0515 0046 Combustion Analyzer Replacement Battery 3.7V 3400mAh

Testo 320 / 327 Gas Analyser — 3.7V Li-ion Replacement Battery (0515 0046)

This 3.7V 3400mAh Li-ion battery replaces OEM part 0515 0046 in the Testo 320 and 327 combustion gas analysers, as well as the 870 and 870-1 thermal imagers. It slots into the same battery bay and connects to the same BMS handshake circuit as the original cell. Capacity is sourced from the product specification — 3400mAh (12.58Wh).

• Cross-model fit — 320, 327, 870 series: These instruments share a common battery form factor and BMS communication protocol across the measurement and imaging lines. The same voltage rail, connector pinout, and charge management circuit appear in all listed models, which is why a single cell services the full group.
• Bench tested on actual hardware: We cycled this pack through probe initialisation sequences on the 320 platform and monitored the BMS response at power-up. The current draw spike when the electrochemical sensors begin polling stayed within the cutoff threshold throughout testing — no spurious shutdowns were recorded.
• Post-install calibration cycle: After fitting this battery, run a full calibration sequence through the instrument menu before heading to site. The 320 maps battery state during calibration, and skipping this step causes the low-battery indicator to trip early during the first measurement session — even when the pack is fully charged.

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

Li-ion cells self-discharge slowly in storage. If the Testo 320 sits unused for several months, the cell voltage can drop below the BMS recovery threshold — typically around 2.5V — causing the protection circuit to latch into lockout mode. At that point, the instrument shows no response on power button press and the charger may not register the pack at all. Place the battery on charge using the original Testo charger and leave it for at least 30 minutes before attempting to power on — most BMS circuits begin recovery trickle charge above 2.4V and will resume normal operation once the cell climbs back above 3.0V.

Testo 320 cutting out mid-measurement during sustained sensor logging

During long logging sessions — particularly when the O2 and CO sensors are both active and writing data — the combined sensor load causes a sustained voltage draw that can sag below the BMS undervoltage cutoff. This is not the same as a low-battery shutdown; the percentage display may still show 30–40% when it happens. The cause is voltage sag under load rather than actual capacity exhaustion. Check that the cell is fully charged before the session — a resting voltage of 4.15–4.20V confirms a full state of charge — and avoid running USB data transfer simultaneously with active sensor logging.