iRobot Roomba S9 Replacement Battery ABL-B 14.4V 4400mAh

iRobot Roomba S9 / S9+ — 14.4V Li-ion Replacement Battery (ABL-B)

This 14.4V, 4400mAh (63.36Wh) lithium-ion battery replaces the original ABL-B pack in the iRobot Roomba S9 and S9+ robotic vacuums, including the S955020 variant. It fits directly into the battery bay and connects to the same BMS handshake the onboard controller expects. Capacity figure is from the product specification — not extrapolated from runtime claims.

• S9 and S9+ compatibility: Both models share the same 14.4V battery bay, connector pinout, and BMS communication protocol. The S9+ adds the Clean Base dock, but the battery draw profile is identical across the two — same voltage rail, same thermal cutoff thresholds, same cell count.
• Bench tested on actual hardware: We ran this pack through full discharge cycles on an S9 unit and confirmed the BMS negotiated correctly with the robot's controller — charge acceptance, low-voltage cutoff, and thermal reporting all responded as expected on the iRobot platform.
• Dock charging behaviour on the S9: Remove the Roomba from the charging dock once the battery reaches full charge. The S9 platform applies a continuous trickle charge when left docked indefinitely. Over weeks, this accelerates cell degradation faster than normal cycle wear. Charge to full, then undock until the next scheduled run.

Suction dropping before the battery indicator reaches low on the S9

The S9's brushroll motor draws peak current on carpet, and a partially blocked filter forces the motor to sustain that draw longer than rated. When sustained current exceeds the BMS threshold, the pack sags below the motor controller's minimum voltage before the fuel gauge registers low. The robot reads this as a normal suction event, not a battery warning. Check and clean the filter first — a clear filter cuts motor draw back to rated levels and the voltage sag disappears.

Roomba S9 shuts down mid-cycle and restarts after a short pause

This is a BMS overcurrent trip, not a dead battery. When the brushroll jams — hair wrap, debris blockage, or a seized side brush — current spikes sharply and the BMS cuts output to protect the cells. The robot pauses, the BMS resets after a few seconds, and the unit restarts. Clear the brushroll and side brush of any obstruction, then re-run the cycle. If the trip recurs without an obvious blockage, check that the brushroll bearing spins freely by hand.