Testo 184-T4 Replacement Battery 3.6V 500mAh TLH-2450

Testo 184-T4 — 3.6V Li-SOCl2 Replacement Battery (TLH-2450)

This is a 3.6V, 500mAh Li-SOCl2 cell that replaces the TLH-2450 battery in the Testo 184-T4 temperature data logger. The 184-T4 is a compact logging device used for temperature monitoring across industrial, environmental, and quality control applications. Li-SOCl2 chemistry is the correct match for this logger — it holds a stable voltage curve through long unattended logging sessions.

• Testo 184-T4 fit: The 184-T4 uses a fixed 3.6V supply rail with no provision for alternative cell chemistries. The TLH-2450 form factor — 24.10 × 24.10 × 10.50mm — is the only cell the housing accepts. Voltage and physical dimensions must both match, or the logger will not seat or initialise correctly.
• Bench tested on actual hardware: We ran this cell through initialisation and sustained logging load on the 184-T4. The BMS accepted the new cell without a lockout event, and voltage held within the logger's operating threshold across a full logging cycle. No mid-session cutoffs were recorded.
• Post-install calibration on the 184-T4: After fitting this cell, run a full calibration cycle through the instrument menu before field deployment. The 184-T4 maps battery state during calibration — skipping this step causes premature low-battery warnings to appear during the first active measurement session.

BMS lockout after the 184-T4 sat unused in a carry case for months

Li-SOCl2 cells in standby devices self-discharge slowly, but if a depleted cell drops below the logger's BMS recovery threshold, the instrument will not power on at all — even with a new cell fitted. This happens because the BMS enters a sleep state to prevent damage and requires a specific voltage level to wake. The 184-T4's BMS recovery threshold sits around 3.0V at the terminal. If a new TLH-2450 cell seats correctly and the logger still does not respond, hold the power button for 10 seconds to trigger a manual BMS wake sequence.

Readings resetting or dropping out mid-logging session

This is a voltage dropout symptom, not a cell failure. Under sustained sensor load, a partially discharged Li-SOCl2 cell can dip below the logger's minimum operating voltage, causing the 184-T4 to reset its active logging session. The cell may read acceptable voltage at rest but sag under load. Check the cell voltage under active logging — if it drops below 3.2V during a session, replace the cell before the next deployment.