Shark XBTR625 Cordless Vacuum Replacement Battery 21.6V 2250mAh

Shark BU3120 / Cordless Detect Pro — 21.6V Li-ion Replacement Battery (XBTR625)

This is a 21.6V, 2250mAh (48.6Wh) Li-ion replacement battery for the Shark BU3120, BU3521, Cordless Detect Pro, IW3110C, and related cordless stick vacuum models. It replaces OEM part numbers XBTR625, XBTR625KDC, XBTR625KSLEU, and XBTR625KSLN. When the original pack loses capacity or stops holding charge, this swap restores the vacuum to working condition.

• BU3120 and Detect Pro series compatibility: These models share a common 21.6V power rail, the same battery connector footprint, and a BMS handshake protocol the charger expects before releasing current. That shared architecture means one battery pack covers the full range listed above without modification.
• Bench tested on actual hardware: We ran this pack under sustained motor load and verified the BMS held voltage through full draw cycles without tripping into protective cutoff prematurely. Cell balance across the pack stayed within tolerance from first charge to discharge.
• Dock charging behaviour on these vacuums: Do not leave the vacuum sitting on the charging dock continuously. These Shark models trickle-charge when left docked indefinitely, which accelerates capacity fade in the cell pack. Charge to full, then remove from the dock until the next use.

Suction dropping before the battery indicator reaches low

On the BU3120, suction loss before the indicator warns of a low battery almost always points to a restricted filter forcing the motor to draw above rated current. The BMS reads that elevated draw as a fault condition and throttles output voltage to protect the cells — not because the pack is depleted. Clean or replace the foam and HEPA filters first. If suction recovers, the battery was never the problem; if it doesn't, check that the pack rests at or above 21.0V under no-load before condemning it.

Motor cuts out mid-use then recovers after a short pause

This is a BMS overcurrent trip, not a failing battery. When airflow is restricted — blocked filter, clogged brush roll, or a sealed floor nozzle — the motor strains and current spikes past the BMS threshold. The pack shuts down to protect the cells, cools briefly, then resets. The fix is clearing the restriction, not replacing the battery. If trips continue on a clean, unblocked vacuum, check the resting pack voltage; anything below 18V at rest points to cell degradation and genuine replacement is warranted.