LG CordZero R9 21.6V Replacement Battery EAC64578401 4000mAh

LG CordZero R9 / R87 Series — 21.6V Li-ion Replacement Battery (EAC64578401)

This 21.6V 4000mAh lithium-ion battery replaces the original power pack on the LG CordZero R9, R9MASTER, R87, and BDV1 cordless stick vacuums. It uses OEM-matched cell geometry and a compatible BMS to maintain normal power delivery to the motor. Capacity is rated at 86.4Wh — sourced to match the original specification.

• R9 and R87 platform fitment: These models share the same 21.6V battery rail, connector pinout, and BMS handshake protocol — one cell covers the full range. The R9MASTER and BDV1 use the same dock and charging circuit, so the same battery seats and communicates correctly across all four variants.
• Bench tested on actual hardware: We cycled this cell on an R9 unit under sustained carpet-mode load. The BMS handled motor-start inrush without tripping, held voltage above the cutoff threshold through a full working cycle, and responded correctly to the dock's charge termination signal.
• Dock charging discipline on the R9 series: Do not leave the vacuum seated on the charging dock between every use. The R9 dock delivers a maintenance trickle charge once full, and continuous trickle exposure degrades cell capacity faster than regular charge-and-remove cycles. Charge to full, then lift it off the dock.

Suction dropping before the battery indicator reaches low on the R9

This happens when the motor draws above its rated current — usually from a partially blocked filter or restricted airflow path — and the BMS begins throttling voltage output to protect the cells before the indicator registers low. The vacuum feels like it's losing suction, but the battery gauge still shows charge. Clean or replace the filter first. If suction recovers immediately, the cell was fine — the filter restriction was forcing the motor to overwork and pull the pack below its stable delivery voltage.

Motor cuts out mid-clean then restarts after a short pause

This is a BMS overcurrent trip, not a cell failure. When sustained suction restriction forces the motor to draw beyond the pack's current ceiling, the BMS opens the circuit to prevent cell damage — then resets after a brief thermal and current recovery window. The restart is the BMS re-closing. Check the filter and brush head for blockages before concluding the battery is at fault. If the motor runs cleanly after clearing the blockage, the pack is operating correctly — the trip threshold on this cell is calibrated to protect it at sustained draws above its rated output.