Midea S60 Replacement Battery 21.6V 4000mAh BP21640A

Midea S60 Series — 21.6V Li-ion Replacement Battery (BP21640A)

This is a 21.6V 4000mAh (86.4Wh) Li-ion replacement battery pack for the Midea S60, S60 Hono, S60 Pro, and S60 Ultra cordless stick vacuums. It slots into the same battery bay and connects through the same BMS handshake as the original BP21640A pack. When the original battery stops holding charge or capacity has dropped noticeably, this is the direct replacement.

• S60 series compatibility: All four S60 variants — standard, Hono, Pro, and Ultra — share the same 21.6V battery platform, connector pinout, and BMS communication protocol. The same pack fits each without modification.
• Bench tested on actual hardware: We cycled this pack through multiple charge and discharge runs on the S60 motor platform. The BMS handled ramp-up current correctly and tripped at the expected overcurrent threshold when suction was restricted — consistent with OEM behaviour.
• Dock charging on the S60: Do not leave the vacuum sitting on the dock permanently. The S60 charging circuit does not fully terminate current when the pack reaches 100%. Continuous dock charging causes capacity fade over weeks. Charge to full, then remove from the dock.

Cordless vacuum losing suction before the battery indicator reaches low

On the S60, suction drop before the battery indicator reads low usually points to voltage sag under motor load — not actual remaining capacity. When the filter is partially blocked, the motor draws above its rated current and the cell voltage dips below the BMS operating threshold, which the indicator does not reflect accurately. The BMS reads instantaneous voltage under load, not state of charge. Clean the filter first — if suction stabilises after that, the battery is fine. If suction still drops on a clean filter with a fresh pack, check the brush roll for hair wrap restricting motor spin.

Motor cuts out mid-clean then recovers after a few seconds

This is a BMS overcurrent trip, not a battery fault. The S60's BMS cuts power when sustained current exceeds its trip threshold — typically triggered by a blocked filter or jammed brush roll forcing the motor to work harder than rated. The few-second recovery time is the BMS reset window. Pull the filter and check the brush roll before assuming the battery is defective. If trips continue on a clear airpath with a new pack, measure the pack voltage immediately after a trip — it should read above 20V. Below that points to cell degradation, not a BMS fault.