AEG FX9 Cordless Vacuum Replacement Battery 36V 2000mAh

AEG FX9 Series — 36V Li-ion Replacement Battery (140144439084)

This is a 36V, 2000mAh (72Wh) lithium-ion replacement battery for the AEG FX9 cordless stick vacuum. It fits the FX9, FX9-1-4IG, FX9-1-4ST, FX9-1-ALRG, and additional variants in the FX9 range. Use it to restore full suction power when the original cell has lost capacity or stopped holding charge.

• FX9 series compatibility: All listed FX9 variants share the same 36V battery architecture, connector pin layout, and BMS handshake protocol. Swapping between variants is not an issue — the voltage rail and communication lines are consistent across the range.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an FX9 chassis. The BMS negotiated correctly with the charger, the over-current trip threshold behaved as expected under simulated motor load, and cell voltage held stable at 36V nominal throughout discharge.
• Dock charging on the FX9: Do not leave the FX9 sitting on its charging dock permanently. Continuous trickle charge accelerates capacity fade in lithium cells faster than intermittent use. Charge to full, then remove the vacuum from the dock until the next use.

Suction dropping before the battery indicator reaches low

The FX9 motor draws significantly more current when airflow is restricted — a partially blocked filter forces the motor to work harder, pulling the cell voltage down faster than normal. The battery indicator reads state-of-charge, not voltage under load, so it can still show two bars while the motor is already starved. You will notice suction recovery if you release the trigger and restart — that is voltage rebounding at rest. Clean or replace the HEPA filter first; if suction stabilises, the battery was being over-drawn by restriction, not failing.

Motor cuts out mid-clean and then restarts after a few seconds

This is a BMS overcurrent trip, not a battery failure. It triggers when sustained current draw — typically on thick carpet or when suction is partially blocked — exceeds the cell's rated discharge threshold. The BMS opens the circuit to protect the cells, then resets once current demand drops. Check the filter and brush roll for blockage before concluding the battery is at fault. If trips persist on a clear filter with a new cell, measure resting voltage after a full charge — it should read between 41V and 42V.