About this replacement
Leica CS20 / GS18 Field Controller — 11.1V Li-ion Replacement Battery (799190)
This 11.1V 3450mAh Li-ion battery pack replaces OEM part numbers 799190, GEB331, GEB333, GEB334, GEB363, and GEB364. It fits the Leica CS20 field controller, CS20 surveying system, and GS18 GNSS antenna units. Voltage and cell count match the original pack exactly to keep the instrument's power management system satisfied.
- CS20 and GS18 shared platform: Both the CS20 controller and GS18 GNSS units draw from the same 11.1V three-cell architecture and use the same connector and BMS handshake protocol — which is why one pack covers both instrument lines without modification.
- Bench tested on actual hardware: We ran this pack through the CS20 boot sequence and instrument initialisation. The BMS communicated state-of-charge correctly, the instrument accepted the pack without a battery fault flag, and cell balancing held stable under sustained GNSS lock load.
- Pre-deployment calibration cycle: After installing this pack, run a full calibration sequence through the CS20 instrument menu before heading to site. The controller maps battery state during that routine — skipping it causes premature low-battery warnings on your first measurement session, even with a fully charged pack.
BMS lockout after the CS20 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 7.5V total — most BMS circuits enter a deep-sleep lockout state as a protection measure. In this state the instrument sees no communication from the pack and will not power on, which looks identical to a dead battery or a fault. The fix is a slow pre-charge using a compatible Leica charger: the charger applies a low-current trickle that nudges cells back above the BMS recovery threshold before full charge resumes. Do not attempt to revive the pack by jump-starting it from an external source — that bypasses the BMS and risks cell damage.
CS20 shuts down mid-session during USB data transfer to a connected PC
USB data transfer adds a draw on top of the active GNSS or total station load — the combined current pull can push the BMS into a protective cutoff if the pack is below roughly 30% charge. The instrument cuts power cleanly rather than letting voltage sag corrupt the data log, so the shutdown is intentional BMS behaviour, not a hardware fault. The fix is straightforward: keep the pack above 50% before starting any transfer session, or connect the instrument to mains via the charging cradle so the transfer draw comes from the charger rather than the cells. Check the cell voltage reads at least 11.0V at transfer start.