AEG QX9-1-40 Cordless Vacuum Replacement Battery 21.6V 2000mAh

AEG QX9-1-40 Series — 21.6V Li-ion Replacement Battery (405 54 78-29/3)

This 21.6V, 2000mAh Li-ion battery pack replaces the original cell in the AEG QX9-1-40, QX9-1-40GG, and QX9-1-P4GG cordless stick vacuums. It fits the same connector and communicates with the same BMS as the factory unit. Capacity matches the original at 43.2Wh — no modifications needed.

• QX9-1-40 series compatibility: All three models in this range share the same 21.6V cell architecture, connector pinout, and BMS handshake protocol. Swapping between them does not require any adapter or firmware change.
• Bench tested on actual hardware: We cycled this pack through the QX9-1-40 motor under sustained load and restricted airflow. The BMS held voltage above cutoff through normal operating draw and tripped cleanly on simulated blockage — no false shutdowns at full suction.
• Dock charging behaviour on the QX9-1-40: Do not leave the vacuum sitting on the charging dock between uses. The QX9-1-40 dock does not stop current when the pack reaches full — continuous trickle charge accelerates capacity fade on Li-ion cells. Charge fully, then remove from the dock.

Suction dropping before the battery indicator reaches low

This happens when the motor is working harder than rated — usually a partially blocked filter forcing higher current draw. That extra draw pulls cell voltage down faster than the indicator tracks, so the vacuum feels weak while the LED still shows two or three bars. The BMS reads actual cell voltage, not the indicator display. Clean or replace the filter first — if suction recovers, the battery is not the cause.

Motor cutting out mid-clean then restarting after a few seconds

This is a BMS overcurrent trip, not a dead battery. When airflow is restricted — by a full dustbin, a clogged filter, or a blocked nozzle — the motor draws a sustained current spike the BMS interprets as a fault. It cuts power to protect the cells, then resets once current drops. Empty the dustbin, clear the filter, and check the nozzle inlet before assuming the battery is faulty. If the problem stops after clearing the restriction, the pack is functioning correctly.