Vernier GDX-BAT-300 Colorimeter Replacement Battery 3.7V 300mAh

Vernier Go Direct Colorimeter & Sensor Series — 3.7V Li-Polymer Replacement Battery (GDX-BAT-300)

This 3.7V, 300mAh Li-Polymer battery fits Vernier Go Direct wireless sensors including the Colorimeter, Conductivity Probe, Drop Counter, and Electrode Amplifier, among others. All of these devices share the GDX-BAT-300 form factor and BMS handshake. Capacity is 300mAh (1.11Wh) as sourced from Vernier's OEM specification.

• Go Direct sensor platform compatibility: Vernier's Go Direct line standardises on this cell across multiple sensor modules because they share the same 3.7V power rail, physical footprint (41.56 × 20.20 × 4.90mm), and BMS communication protocol — so one replacement pack covers the full sensor range listed above.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on Go Direct hardware and confirmed the BMS handshake completes correctly, charge termination triggers at full cell voltage, and the protection circuit trips cleanly on overcurrent — no false cutoffs under normal sensor load.
• Post-install calibration on Go Direct sensors: After fitting this battery, run a full calibration cycle through the Vernier Graphical Analysis app before your first lab session. The sensor maps battery state during calibration, and skipping this step causes premature low-battery warnings mid-experiment.

GDX-BAT-300 BMS lockout after a Go Direct sensor sat unused in storage

Li-Polymer cells self-discharge slowly during storage. If a Go Direct sensor sits unused for several months, the cell can drop below the BMS recovery threshold — typically around 2.5V — and the protection circuit latches off. At that point the device shows no signs of life and will not respond to a standard charge attempt. Connecting via USB to a 5V source for 15–30 minutes allows the charger IC to trickle-charge the cell back above the recovery threshold, after which normal charging resumes. If the cell has dropped below 2.0V, the BMS may not recover and the pack should be replaced.

Colorimeter shuts off during Bluetooth data transfer to a tablet

The Go Direct Colorimeter draws current from two sources simultaneously during an active Bluetooth session: the LED light source and the wireless radio. On a degraded or partially discharged cell, this combined load pulls the terminal voltage below the BMS cutoff threshold, triggering an abrupt shutdown even when the battery indicator still shows charge. The voltage-threshold indicator on this platform is calibrated to an open-circuit reading, not a load-adjusted one, so the displayed percentage is optimistic under dual load. Charge the battery fully before long logging sessions, and check that the cell voltage reads at or above 3.7V on a multimeter before connecting.