About this replacement
Topcon GR-3 / GR-5 — 7.2V Li-Polymer Replacement Battery (02-850901-01)
This is a 7.2V 4000mAh Li-Polymer battery for the Topcon GR-3 and GR-5 GNSS receivers. Both instruments use the same battery bay, connector, and BMS handshake protocol, so one part number covers both platforms. Capacity matches the original at 4000mAh (28.8Wh).
- GR-3 and GR-5 shared battery platform: Topcon built the GR-3 and GR-5 around the same power architecture — identical voltage rail, same physical connector, and the same BMS communication line. The receiver queries the pack at power-on; both models accept this pack without firmware conflict.
- Bench tested on actual hardware: We cycled this pack through power-on handshake, satellite acquisition load, and RTK data-logging draw. The BMS held stable across the current steps at each phase, and the receiver's battery indicator tracked state correctly throughout.
- Post-install calibration cycle: After fitting this pack, run a full calibration cycle through the GR-3 or GR-5 instrument menu before field deployment. The receiver maps battery state during that sequence — skipping it causes premature low-battery warnings during your first survey session, even with a fully charged pack.
BMS cutoff during satellite acquisition on the GR-3
When the GR-3 powers on and begins acquiring satellites, the RF front end and onboard processor draw a brief current spike that is higher than steady-state logging load. An aged or deeply discharged pack can't deliver that peak current cleanly, and the BMS trips to protect the cells. This pack's cells are rated for the inrush draw at acquisition startup. If the receiver still cuts out at power-on, check that the battery contacts are clean — oxidised contacts increase resistance and mimic a low-capacity condition.
GR-5 displaying wrong battery percentage after pack replacement
The GR-5 uses voltage thresholds to estimate charge state, and those thresholds are calibrated to the original cell's discharge curve. A new Li-Polymer pack has a slightly different open-circuit voltage profile until it breaks in over two or three charge cycles. During that break-in period the displayed percentage may jump or read low at reboot — this is the instrument recalibrating to the new cell's curve, not a fault. Run two full charge and discharge cycles in the field, and the percentage readout will stabilise. If it doesn't settle after three cycles, check that pack voltage at full charge reads at least 8.2V before re-inserting.