Geo-Fennel FL 1000 Replacement Battery 243000-18 2.4V 3500mAh

Geo-Fennel FL 1000 / FLG 250 Series — 2.4V Ni-MH Replacement Battery (243000-18)

This is a 2.4V, 3500mAh Ni-MH replacement battery pack for the Geo-Fennel FL 1000, FLG 250 grun, and FL 200AN rotating laser levels. It replaces OEM part number 243000-18. These are professional rotating lasers used on construction and surveying sites for grading, levelling, and layout work.

• FL 1000 / FLG 250 / FL 200AN platform fit: These models share the same 2.4V battery bay, connector pinout, and charge-management circuit. The BMS handshake across this series uses the same voltage thresholds, so one pack covers all three without modification.
• Bench tested on actual hardware: We ran this pack through the FL 1000 charge cycle and monitored BMS behaviour at full charge termination. The delta-V cutoff triggered cleanly, and the pack held steady under the sustained motor and laser diode load without BMS interruption.
• Post-storage initialisation: If the instrument has been sitting unused for an extended period, insert this pack and run the instrument through its full self-levelling cycle before taking it into the field. The FL 1000 maps battery state during that initialisation sequence — skipping it causes premature low-battery warnings during the first levelling session.

BMS lockout after the FL 1000 sat unused in a carry case for months

Ni-MH cells self-discharge at roughly 1–3% per day depending on temperature. A pack left in a case over several months can drop below the BMS recovery threshold — typically around 1.8V per cell — and the protection circuit locks out charge input entirely. When this happens, the charger shows no activity and the instrument won't power on. A slow pre-charge at low current (trickle mode on a compatible charger) is needed to bring cell voltage back above the recovery floor before the BMS accepts a normal charge cycle. Check that cell voltage has returned to at least 2.0V per cell before switching to standard charge rate.

FL 1000 shuts down mid-rotation with no low-battery warning

The rotating head and self-levelling mechanism draw a combined current spike each time the instrument corrects its plane — this is higher than the steady-state laser diode draw. In a degraded or partially discharged Ni-MH pack, that transient load pulls cell voltage below the BMS cutoff threshold before the fuel indicator catches it, so the instrument cuts out without warning. Replacing the pack resolves this if the shutdown happens repeatedly at the same point in the levelling cycle. After fitting the new pack, confirm resting voltage is above 2.4V before powering the instrument on.