Leica CS35 Controller 10.8V Replacement Battery GEB235

Leica CS35 Controller — 10.8V Li-Polymer Replacement Battery (GEB235 / GEB236)

This is a 10.8V, 4100mAh (44.28Wh) lithium-polymer battery for the Leica CS35 field controller. The CS35 is a handheld data collector used by surveyors and construction professionals for positioning and measurement tasks. This cell replaces OEM part numbers GEB235 and GEB236.

• CS35 platform fit: The GEB235 and GEB236 share the same 10.8V three-cell Li-Polymer configuration, connector pinout, and BMS handshake protocol. Both part numbers slot into the same battery bay on the CS35 controller without hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under CS35 load conditions. The BMS communicated correctly with the controller, state-of-charge reporting was stable, and thermal cutoff thresholds responded as expected during high-draw GPS acquisition bursts.
• First-cycle calibration on the CS35: After fitting this battery, run the CS35 until it shuts down at the low-voltage cutoff, then charge it to 100% without interruption. The controller's fuel gauge IC needs this full cycle to anchor its charge estimation to the new cell's actual capacity curve.

CS35 reporting battery health as poor immediately after swap

The CS35 controller reads health data from EEPROM embedded in the battery's BMS. When a new cell is installed, the EEPROM contains factory defaults that the controller interprets as degraded relative to its stored baseline. This is not a fault with the replacement cell — it is a mismatch between the old learned data and the new cell's profile. Run one full discharge-to-cutoff followed by an uninterrupted charge to 100%. After one or two complete cycles, the controller recalibrates its battery learn cycle and the health warning clears.

CS35 shutting down with 20–30% charge still shown on screen

This happens when the fuel gauge IC's discharge curve no longer matches the cell's actual voltage behaviour under load. The CS35's GPS receiver, display, and wireless radio draw current simultaneously, creating brief high-demand spikes. At that load level, an uncalibrated cell can hit the BMS low-voltage cutoff at 9.9V while the screen still shows a non-zero percentage. The fix is a supervised full discharge to hibernate-cutoff followed by a complete, uninterrupted charge — this anchors the fuel gauge IC to the cell's real voltage cliff point.