About this replacement
Leica TPS1000 / TC400–905 Series — 12V Ni-MH Replacement Battery (GEB77)
This is a 12V, 1200mAh Ni-MH battery replacing the Leica GEB77 (OEM ref 439149). It fits the TPS1000 total station and TC400–905 series instruments used for field surveying and construction layout. Voltage and connector match OEM spec — the instrument's power management circuit will accept the pack without modification.
- TPS1000 and TC400–905 compatibility: Both series run the same 12V power rail and use the same GEB77 bay connector. The BMS handshake protocol is identical across this range, so one pack covers the full lineup without adapter or firmware workaround.
- Bench tested on actual hardware: We cycled this pack under a simulated EDM and servo load — the combined draw a TPS1000 pulls during a motorised measurement sequence. The BMS held the output rail steady and did not trip on the servo initialisation spike.
- Pre-deployment calibration cycle: After installing this pack, run a full calibration cycle through the TPS1000 instrument menu before taking it to site. The instrument maps battery state during that routine — skip it and you will see premature low-battery warnings on the first measurement session even with a full charge.
Why the TPS1000 shuts down at the start of a measurement sequence
The TPS1000 powers the EDM module and the servo drive simultaneously when a measurement is triggered. That combined inrush — particularly on motorised TC-series instruments — creates a brief but sharp current spike. An aged or deeply discharged pack cannot sustain the voltage through that spike, so the BMS drops the circuit as a protection response. A new, fully charged pack with healthy internal resistance handles the spike without the voltage rail collapsing below the cutoff threshold.
Instrument reads partial charge immediately after a full charge cycle
Ni-MH cells in a new or long-stored pack often have uneven cell voltages across the stack. The TPS1000 reads pack voltage at startup and maps that to a charge percentage — if the cells have not been balanced by a proper charge cycle, the voltage sits lower than a fully balanced pack and the display reflects that. Run two full charge-discharge cycles through a Leica GKL112 or equivalent charger before trusting the on-screen indicator. After conditioning, the instrument's threshold calibration aligns to the pack's actual resting voltage at 12V nominal.