AEG FX9 Cordless Vacuum Replacement Battery 36V 3000mAh

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

This is a 36V, 3000mAh Li-ion battery for the AEG FX9 cordless stick vacuum range. It fits the FX9-1-4IG, FX9-1-4ST, FX9-1-ALRG, and six additional FX9 variants that share the same battery bay and connector. Voltage and capacity match the original specification exactly.

• FX9 platform compatibility: All FX9 variants in this fit list run the same 36V motor rail and use the same physical latch and contact arrangement. The BMS handshake protocol is consistent across the range, so a single cell covers the full FX9 lineup without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an FX9 unit. The BMS communicated correctly with the charger, accepted a full charge without error, and released current to the motor without tripping overcurrent cutoff under normal suction load.
• Dock charging habit on the FX9: Do not leave the FX9 sitting on the charging dock between uses. Continuous dock contact causes the charger to apply a trickle current even after the cell is full. Over weeks, this degrades cell capacity noticeably. Charge to full, then remove the vacuum from the dock.

Suction dropping before the battery indicator reaches low

This happens when the motor draws more current than the BMS expects — usually because the filter is partially blocked. Restricted airflow forces the motor to work harder, pulling higher amperage and causing voltage to sag under load. The BMS reads this sag as a low-cell condition and reduces power output before the indicator registers a problem. Clean or replace the filter first; if suction restores and holds, the cell is not at fault.

Motor cutting out briefly then recovering during use

This is a BMS overcurrent trip, not a dead battery. It typically occurs when sustained suction restriction — blocked filter, sealed floor nozzle, or trapped debris — keeps current draw above the BMS threshold for more than a few seconds. The BMS cuts the circuit to protect the cells, then resets automatically. Clear the blockage, confirm the filter is clean, and check that the floor head is not sealed against a surface. If the trip still occurs on an unblocked machine, measure resting cell voltage — it should read at or above 37V after a full charge.