Carlson BRx7 Survey Instrument Replacement Battery 7.4V 2600mAh

Carlson BRx7 / Hemisphere S631 — 7.4V Li-ion Replacement Battery

This 7.4V 2600mAh (19.24Wh) lithium-ion battery fits the Carlson BRx7 handheld data collector, the Base Receiver Smart Antenna Total Station, and the Base Rover Receiver Hemisphere S631. All three units share the same voltage rail, physical form factor, and BMS handshake protocol. Capacity figures come from the product data — not from third-party claims.

• BRx7, Base Receiver, and S631 compatibility: These units run the same 7.4V battery bus with a matching connector pinout and BMS communication line. Swapping between them does not require a firmware change — the instrument reads pack state through the same data pin on all three platforms.
• Bench tested on actual hardware: We ran this pack through a simulated survey session — powering satellite acquisition, active GNSS logging, and Bluetooth data transfer simultaneously. The BMS held the output rail steady through the combined draw without triggering an overcurrent cutoff.
• Field deployment prep for survey instruments: After fitting this pack, navigate to the instrument's battery calibration or system check menu before heading to site. The BRx7 maps voltage thresholds to percentage during this step — skipping it causes the low-battery warning to fire early on the first logging session.

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

Li-ion cells self-discharge slowly in storage. If the pack voltage drops below roughly 2.5V per cell — around 5.0V total for a 2S pack — the BMS trips a deep-discharge lockout and the instrument will not power on even with a charger connected. Standard chargers see zero voltage at the terminals and refuse to initiate a charge cycle. To recover, use a charger with a manual "boost" or "recovery" mode that can push a low-current pulse (around 100mA) until cell voltage climbs above 3.0V per cell, at which point normal charging resumes.

BRx7 shuts down instantly when satellite acquisition starts

GNSS acquisition draws a brief but sharp current spike as the RF front-end and correlator circuits initialise — this can exceed the BMS overcurrent threshold on a degraded or partially discharged pack, triggering an immediate cutoff. The instrument appears to power on normally, then drops dead the moment it starts scanning for satellites. Charge the pack fully to 8.4V before the next attempt, then power on the BRx7 with the survey app already closed so the RF module does not initialise until the voltage rail is stable.