About this replacement
Philips FC6401 / PowerPro Aqua — 18.5V Li-ion Replacement Battery (INR18650X25)
This 18.5V Li-ion battery replaces the OEM pack in the Philips FC6401, FC6402, and PowerPro Aqua stick vacuum cleaner range. Capacity is 2500mAh (46.25Wh) — matching the original specification. It fits the FC6401/01 and related variants that share the same battery housing and connector.
- FC6401 / FC6402 / PowerPro Aqua compatibility: These models run the same 18.5V motor rail and use an identical battery footprint, connector pin-out, and BMS communication protocol. One cell pack covers the full group.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on an FC6401 unit. The BMS handshook correctly with the Philips charger, and overcurrent protection tripped as expected under a simulated blockage load before recovering cleanly on restart.
- Dock charging on the PowerPro Aqua: Do not leave the vacuum sitting on the charging dock continuously. The Philips dock does not cut trickle charge once full, and sustained low-current charge degrades cell capacity faster than normal cycle wear. Charge to full, then remove from the dock.
Suction dropping before the battery indicator reaches low
The FC6401 motor draws harder when the filter is partially blocked — pulling more current than the BMS expects under normal load. This causes the battery voltage to sag earlier than the indicator reflects, and suction weakens noticeably while the LED still shows adequate charge. The indicator measures resting cell voltage, not load voltage, so the two can diverge. Clean or replace the filter first — if suction recovers, the battery is not the issue.
Motor cuts out mid-clean then restarts after a short pause
This is a BMS overcurrent trip, not a dead battery. When the vacuum runs with a blocked filter or a restricted nozzle, sustained high current draw pushes past the BMS protection threshold and the pack shuts output. The vacuum goes silent, then recovers after the BMS resets — usually within 10 to 30 seconds. Clear the blockage, check the filter, and restart. If the trip keeps recurring with a clean filter, measure resting pack voltage — it should read at or above 18.5V after a full charge.