Stonex S3 GNSS Replacement Battery 7.4V 2200mAh BP-3

Stonex S3 / S9 GNSS Series — 7.4V Li-ion Replacement Battery (BP-3)

This is a 7.4V 2200mAh Li-ion battery for the Stonex S3, S8 Plus GNSS, S9, and S9 GNSS receivers. It replaces OEM part numbers BP-3, BT-L72SA, BT-L74SA, and BT-S9374. These are professional GNSS survey instruments used in the field for precision positioning and spatial data capture.

• S3, S8 Plus, S9 and S9 GNSS compatibility: These four receivers share the same 7.4V battery platform, connector pinout, and BMS handshake protocol — one pack fits the full range without modification.
• Bench tested on actual hardware: We ran this pack through the S9 GNSS receiver under active satellite acquisition load. The BMS held steady through the GNSS module power-up spike and maintained stable voltage delivery during continuous logging.
• Post-install calibration on first field use: After fitting this pack, run a full system calibration cycle through the instrument menu before deploying on a survey. The S9 series maps battery state during calibration — skipping this step causes premature low-battery warnings during your first logging session even when the pack is fully charged.

BMS lockout after the S9 GNSS sat unused in a carry case for months

Li-ion cells self-discharge over time. If a pack sits long enough, cell voltage can drop below the BMS recovery threshold — typically around 2.5V per cell on a 7.4V (2S) pack. At that point, the BMS enters a protection lockout state and blocks charging current entirely. Standard chargers see this as a missing or faulty pack and show no charge activity. To recover, use a charger with a trickle or recovery mode that feeds a low current — around 0.1C — until cell voltage climbs above 3.0V per cell, then normal charging resumes.

Readings drifting or session data resetting mid-log on the S9 GNSS

Under sustained GNSS tracking load combined with active data logging, current draw is steady but unforgiving — any voltage sag past the receiver's cutoff threshold triggers an abrupt shutdown and session data loss. This is not a firmware fault; it is a cell-level voltage drop under load, usually in an aged or partially discharged pack. Check resting voltage before deployment — a healthy 7.4V Li-ion pack should read 8.2V–8.4V fully charged. If resting voltage is below 7.6V before you start, the pack does not have enough headroom to sustain a full logging session.