About this replacement
Testo 320 Combustion Analyzer — 3.7V Li-ion Replacement Battery (0515 5046)
This 3.7V, 2600mAh Li-ion cell replaces the OEM pack in the Testo 320 Combustion Analyzer. It fits the 320 series used by heating engineers and technicians for on-site boiler and furnace diagnostics. Voltage and capacity match the original specification: 3.7V nominal, 9.62Wh.
- Testo 320 series fit: The 320 platform runs a single-cell 3.7V Li-ion configuration with a specific BMS handshake tied to the instrument's fuel gauge circuit. This replacement uses a matching connector and cell footprint so the instrument reads charge state correctly from first boot.
- Bench tested on actual hardware: We ran this pack through the 320's initialisation sequence and monitored BMS response during probe power-up — the current spike at sensor activation stayed within the pack's protection threshold with no nuisance cutoff.
- Post-install calibration step: After installing, run a full calibration cycle through the instrument menu before field deployment. The 320 maps battery state during calibration, and skipping this step causes premature low-battery warnings during your first measurement session.
Testo 320 shutting down mid-measurement with a charged battery
The 320's flue gas sensors draw a sustained load during active logging that differs from the idle draw the instrument uses to estimate remaining charge. If the cell has degraded or the BMS has not calibrated to the new pack, the protection circuit can read a voltage sag as a low-cell event and cut output. This is not a faulty battery — it is the BMS responding to a real instantaneous voltage drop under sensor load. Running one complete charge-discharge cycle after installation lets the BMS establish accurate cutoff thresholds for the 2600mAh cell.
Pack will not charge after months unused in the carry case
Li-ion cells self-discharge at roughly 2–3% per month at room temperature. A pack stored in the carry case for six months or more can drop below the BMS recovery threshold — typically around 2.5V per cell — causing the charger to refuse the pack entirely. Place the instrument on the Testo docking charger and leave it connected for at least 30 minutes without interruption; many BMS circuits include a trickle pre-charge mode that recovers cells down to approximately 2.0V. If the charge LED does not activate after 30 minutes, the cell has dropped below the recovery floor and the pack needs replacement.