Geo-Fennel FLG 250 Green Laser Level Replacement Battery 2.4V

Geo-Fennel FLG 250 green — 2.4V Ni-MH Replacement Battery

This is a 2.4V Ni-MH battery rated at 3500mAh (8.4Wh), built to replace the original pack in the Geo-Fennel FLG 250 green rotary laser level. The FLG 250 green is a compact construction laser used for levelling and alignment on job sites. This battery powers the rotation motor and levelling functions throughout the working day.

• FLG 250 green fit: The FLG 250 green runs a 2.4V two-cell Ni-MH pack with a specific connector orientation and physical envelope — 100mm × 27.54mm × 25.60mm. The BMS in this laser monitors cell voltage directly, so matching chemistry and cell count matters. Swapping to lithium chemistry without a voltage-matched BMS would cause incorrect charge termination and potential damage to the instrument's charge circuit.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the FLG 250 green platform. The BMS accepted the pack without error flags, and the rotation motor started cleanly on each cycle. Cell balance across the two Ni-MH cells stayed within 30mV throughout sustained load testing.
• Post-install calibration: After fitting this battery, run a full calibration cycle through the FLG 250's instrument menu before taking it to site. The laser maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session, even with a full charge.

BMS lockout after the FLG 250 green sat unused in a carry case for months

Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. After several months in storage, a pack can drop below the BMS recovery threshold — typically around 1.8V total for a 2.4V two-cell pack. When the voltage drops that low, the BMS enters a protective sleep state and the charger may show no activity. To recover the pack, connect it to the charger and leave it for at least 30 minutes — most chargers apply a trickle current to bring voltage back above the recovery threshold before switching to normal charge mode.

FLG 250 green showing low-battery warning immediately after a new pack is fitted

This happens when the instrument's battery indicator is still calibrated to the discharge curve of the old, degraded pack. The voltage-threshold indicator needs a full charge-discharge cycle to recalibrate to the new cells. Charge the new pack fully, then run the laser through normal operation until it shuts down on low voltage — the indicator will read accurately from the next charge cycle onwards. Target a full charge endpoint of 2.88V (1.44V per cell) before starting this conditioning cycle.