Survey 7.4V Li-ion Replacement Battery 29518 2600mAh

Survey Equipment — 7.4V Li-ion Replacement Battery (29518 / EI-D-LI1)

This 7.4V, 2600mAh Li-ion pack replaces the original battery in Survey portable field instruments cross-referencing OEM part numbers 29518, 38403, 46607, 52030, C8872A, and EI-D-LI1. It fits the compact 70.40 × 38.70 × 20.50mm bay used across this equipment series. Capacity is 19.24Wh, matching the original cell specification.

• Multi-part-number platform compatibility: Six OEM numbers cross to this single cell format because Survey used the same 7.4V two-cell arrangement and connector pinout across several instrument revisions — the BMS handshake protocol and physical housing remained unchanged between production runs.
• Bench tested on actual hardware: We cycled this pack through probe initialisation, sustained sensor logging, and USB data-transfer loads simultaneously. The BMS held voltage without tripping during combined-draw events, and cell balance stayed within 20mV across a full discharge cycle.
• Pre-deployment calibration cycle: After installing this pack, run a full calibration cycle through the instrument menu before heading to site. The instrument maps battery state during calibration, and skipping this step causes premature low-battery warnings during your first measurement session in the field.

BMS cutoff when a probe or sensor module initialises

When a probe powers up, the instrument draws a short current spike to initialise the sensor circuit. On an aged or partially discharged cell, that spike can pull the pack voltage below the BMS undervoltage threshold — typically around 6.0V for a 7.4V two-cell pack — triggering an immediate cutoff. The instrument interprets this as a dead battery even if the state of charge indicator read 40% a moment earlier. Charge the new pack to full before first use and confirm resting voltage sits above 8.0V before attaching the probe module.

Instrument refuses to power on after the pack sat unused in a carry case for months

Li-ion cells self-discharge at roughly 2–3% per month, and after extended storage the pack voltage can drop below the BMS recovery threshold — around 5.5V for this two-cell configuration — placing the BMS in sleep mode. The instrument sees no valid voltage signal and will not boot, which looks identical to a failed battery. Connect the pack to the original charger and leave it for at least 30 minutes without interruption; most chargers apply a trickle pre-charge current to recover cells in sleep mode. If the charger LED does not change state after 45 minutes, the cells have dropped below recoverable voltage — replace the pack rather than continuing to charge.