About this replacement
Topcon GTS-600 Series — 7.2V Ni-MH Replacement Battery (BT-50Q)
This is a 7.2V, 2700mAh Ni-MH replacement for the Topcon BT-50Q battery pack. It fits the GTS-600, GTS-601, GTS-602, and GTS-605 total stations — the series used across construction layout, civil engineering, and land surveying. Capacity is 19.44Wh, matching the original specification.
- GTS-600 series compatibility: The GTS-600, GTS-601, GTS-602, and GTS-605 share the same battery bay geometry, voltage rail, and connector pinout. All four models draw from the same 7.2V bus to power the EDM, angle encoders, and display simultaneously. One pack fits all four without modification.
- Bench tested on actual hardware: We cycled this pack through full charge and discharge on a GTS-series unit and monitored the BMS response during EDM activation — the highest instantaneous draw event. The pack held voltage above the cutoff threshold through repeated measurement bursts without triggering a protection event.
- First-use calibration on the GTS-600: After installing this pack, run a full calibration cycle through the instrument menu before heading to site. The GTS-600 maps battery state during calibration — skip this step and the low-battery warning will fire early on your first measurement session, even with a full charge.
EDM pulse triggering BMS cutoff on the GTS-600
The electronic distance measurement module on the GTS-600 draws a sharp current spike every time it fires a pulse toward a prism. On a degraded or deeply discharged Ni-MH pack, this spike can push the cell voltage below the BMS protection threshold for a fraction of a second — enough to trigger a shutdown. A new pack with full cell capacity absorbs this spike without the voltage rail collapsing. If the instrument is shutting off during distance measurements but not during angle-only readings, the battery is the first thing to replace.
GTS-600 not recognising a new pack after it sat unused for months
Ni-MH cells self-discharge over storage. If this pack sat in a warehouse or a carry case for an extended period, cell voltage may have dropped low enough for the BMS to enter sleep mode. The instrument then sees no response on the battery communication line and will not power on. Put the pack on a dedicated Ni-MH charger — not the instrument's internal charger — and let it run a full charge cycle. Once cell voltage recovers above approximately 6.0V, the BMS wakes and the instrument will recognise the pack normally.