Whitlock DNFT Survey Battery 3.6V 1200mAh Li-SOCl2

Whitlock DNFT Series — 3.6V Li-SOCl2 Replacement Battery (000505)

This is a 3.6V 1200mAh lithium thionyl chloride cell replacing OEM part 000505 in the Whitlock DNFT and DNFT-PRG survey and test instruments. Li-SOCl2 chemistry holds a stable voltage curve across the full discharge cycle, which matters when the instrument is logging measurements in the field. Dimensions are 32.00 × 14.60 × 14.60mm — verify these against your existing cell before ordering.

• DNFT and DNFT-PRG compatibility: Both models run the same 3.6V power rail and use identical connector and cell geometry. The DNFT-PRG adds programming functionality, but the battery circuit is unchanged — same voltage threshold, same BMS handshake requirement.
• Bench tested on actual hardware: We ran this cell through probe initialisation cycles and sustained sensor load on the bench. The BMS held stable through the current spike at probe power-up, and voltage output stayed within the instrument's accepted window under continuous logging draw.
• Post-installation calibration on the DNFT: After fitting this cell, run a full calibration cycle through the instrument menu before field deployment. The DNFT maps battery state during calibration. Skip this step and the instrument will throw premature low-battery warnings on the first measurement session.

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

Li-SOCl2 cells have extremely low self-discharge, but the instrument's BMS has a minimum recovery voltage threshold. If the original cell dropped below that threshold during long storage, the BMS enters a sleep state and refuses to accept a new cell until it sees a valid voltage at the terminals. Fitting a fresh 000505 cell should present 3.6V and wake the BMS immediately. If the instrument still shows no response, remove the cell, wait 30 seconds, and reinsert — this forces the BMS to re-poll the terminal voltage from a cold state.

Readings drifting or logging session resetting mid-measurement

This is a voltage dropout issue, not a calibration fault. Under sustained sensor load, a weakened or near-depleted cell can sag below the instrument's minimum operating voltage, causing the DNFT to reset the active logging session. The cell voltage may recover once load drops, so the instrument powers back on and appears fine — masking the root cause. If mid-session resets are happening, check terminal voltage under load; anything reading below 3.2V under active sensor draw means the cell needs replacing.