Topcon BT-24QW GTS-3 Replacement Battery 7.2V 2700mAh

Topcon GTS-3 / GTS-3A — 7.2V Ni-MH Replacement Battery (BT-24QW)

This is a 7.2V, 2700mAh Ni-MH replacement for the Topcon BT-24QW battery pack. It fits the GTS-3 and GTS-3A total stations — theodolite and EDM instruments used in surveying and construction layout. Capacity is rated at 19.44Wh and matches the original pack specification.

• GTS-3 and GTS-3A compatibility: Both models share the same battery bay geometry, voltage rail, and BMS handshake protocol. The connector orientation and cell count are identical across the GTS-3 and GTS-3A platforms, so one pack covers both instruments.
• Bench tested on actual hardware: We cycled this pack through the GTS-3 charge circuit and confirmed the BMS accepted the cell chemistry without triggering a fault flag. The instrument completed a full charge cycle and passed the battery status check on the instrument display.
• Calibration cycle before first field use: After installing this pack, run a full calibration cycle through the instrument menu before deploying to site. The GTS-3 maps battery state during calibration. Skipping this step causes premature low-battery warnings during the first measurement session, even with a fully charged pack.

BMS lockout after the GTS-3 sat unused in a carry case for months

Ni-MH cells self-discharge at roughly 1–3% per day at room temperature. After several months in storage, pack voltage can drop below the BMS recovery threshold — typically around 6.0V for a 7.2V Ni-MH pack. When this happens, the charger may not initiate a charge cycle because the BMS presents the pack as faulty rather than deeply discharged. Some chargers include a recovery or trickle mode that applies a low current to bring the cell voltage back above the threshold before switching to normal charge. If the Topcon charger does not recover the pack automatically, try a compatible Ni-MH charger with an explicit recovery function, then return to the standard charger once voltage reads above 6.5V.

GTS-3 shuts down mid-angle measurement with no low-battery warning

This happens when the EDM module fires and the combined current draw — servo motor, EDM emitter, and display — causes a brief voltage sag that the BMS reads as a fault condition. It is not a capacity problem; it occurs most often with aged or partially discharged cells where internal resistance has increased. A freshly charged pack at full capacity reduces internal resistance and keeps the voltage rail stable under that spike load. If shutdowns continue after a full charge, check that the battery contacts on the instrument bay are clean and making full contact — resistance at the connector adds to the sag.