Carlson BRx7 Survey Receiver Replacement Battery 7.4V 3400mAh

Carlson BRx7 / Base Receiver Smart Antenna / S631 — 7.4V Li-ion Replacement Battery

This 7.4V, 3400mAh Li-ion battery replaces the internal pack in the Carlson BRx7, Base Receiver Smart Antenna Total Station, and Hemisphere S631 Base Rover Receiver. These are field-grade GNSS and survey instruments used in construction layout and land surveying. The pack delivers 25.16Wh at the correct voltage rail for each device.

• BRx7, Base Receiver, and S631 platform fit: These three units share the same 7.4V nominal voltage rail, cell footprint, and connector orientation. The BMS in each instrument communicates with the pack during power-on — the cell chemistry and protection circuit thresholds have to match, or the instrument reports a fault before the first satellite lock.
• Bench tested on actual hardware: We cycled this pack through a full charge and discharge sequence, monitoring BMS handshake signals at power-on. The protection circuit responded correctly to both low-voltage cutoff and overload events without tripping a lock state.
• Field calibration before first deployment: After installing, run a full calibration cycle through the instrument menu before heading to site. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings during the first measurement session, even with a full charge.

BMS lockout after the BRx7 sat unused in a carry case for months

Li-ion cells self-discharge slowly during storage. If the pack voltage drops below approximately 2.5V per cell — around 5.0V at pack level — the BMS enters a sleep state and blocks normal charging to protect the cells. Plugging into the standard charger at this point shows no charge activity, or the charger LED cycles without progress. To recover, apply a slow pre-charge current from a compatible charger that supports a recovery or wake mode until pack voltage climbs above 6.0V, then resume normal charging.

Readings drifting or logging session resetting mid-survey

Sustained GNSS tracking, active base station communication, and simultaneous data logging create a combined current draw that can cause momentary voltage sag on an aged or partially discharged pack. When the voltage dips below the instrument's brown-out threshold, the processor resets to protect the firmware state — this looks like a spontaneous reboot or a gap in the log file. A new pack holds a flatter discharge curve under this sustained load. Confirm the replacement pack is charged above 7.2V before starting a logging session.