Rokamat FOX 18V Replacement Battery 2000mAh Li-ion

Rokamat FOX / DRAGONFLY / WDVS-Sauger — 18V Li-ion Replacement Battery

This 18V 2000mAh (36Wh) Li-ion battery replaces the original pack on the Rokamat FOX, DRAGONFLY, WDVS-Sauger, and FILZER cordless tools. These are concrete grinding, polishing, and surface preparation machines — high-vibration, high-draw tools that cycle their motors hard. Drop voltage at the cell level and the BMS will pull the pack offline mid-pass.

• FOX / DRAGONFLY / FILZER platform fit: These models share the same 18V battery rail and connector format. The BMS handshake protocol is consistent across the platform, so one pack services the full lineup without adapter or firmware mismatch.
• Bench tested on actual hardware: We cycled this pack under simulated motor-start inrush loads typical of a concrete grinder. The BMS held the overcurrent threshold correctly and did not trip on the initial trigger pull surge. Cell balance across the pack stayed within 20mV after five full discharge cycles.
• First-use conditioning on grinding tools: On first use, run the grinder at half load for two cycles before full-torque grinding passes. This lets the BMS profile the motor's inrush current draw and set its overcurrent protection thresholds accurately before you hit it with a full concrete surface pass.

BMS cutoff on motor-start inrush with the FOX grinder

Concrete grinders pull a sharp current spike the instant the motor starts — this inrush can be three to five times the running draw. A BMS that hasn't profiled the motor yet may read that spike as a fault and cut the pack offline immediately. This is more common with a new or fully rested battery where the BMS has no prior inrush data logged. Running two half-load cycles first teaches the BMS where the real fault threshold sits versus a normal start event.

Pack drops out under sustained grinding load but recovers at rest

If the tool cuts out after several continuous passes but powers back on after a short rest, the cause is thermal cutoff — not a dead cell. The grinder motor generates heat, and that heat transfers into the battery housing during extended use. Once cell temperature crosses the BMS thermal limit, the pack disconnects to protect the cells. Let the pack cool for 10–15 minutes, then check the battery housing for heat before resuming. If cutouts happen within the first few passes, check rail contact resistance — oxidised terminals cause voltage sag that mimics thermal shutdown.