Adaptec BAT-00011-01-A RAID Controller Compatible Battery 3.7V 1800mAh

Adaptec Serial Attached SCSI RAID Controllers — 3.7V Li-ion Replacement Battery (BAT-00011-01-A)

This 3.7V, 1800mAh Li-ion cell replaces the backup cache battery in Adaptec RAID controller cards, including the 4800SAS, 4805SAS, and 2218300-R. It powers the controller's cache module during an unexpected power loss, holding in-flight write data until the system recovers. Without a functional cell, the controller drops to write-through mode and cache-backed write performance is gone.

• 4800SAS / 4805SAS / 2218300-R compatibility: These controllers share the same cache backup architecture and use the same connector pinout and BMS handshake protocol, which is why one cell covers the group. Voltage tolerance on the backup rail is narrow — the BMS will reject a cell outside its acceptance window at initialisation.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a live controller. The BMS accepted the cell, completed its initialisation handshake, and the backup window was calculated after the learn cycle finished. No fault codes were thrown post-cycle.
• Post-swap learn cycle: After fitting the new cell, initiate the battery learn cycle from your controller management interface — StorCLI: /cx bbu show; ONTAP: system controller battery show. The controller holds in write-through mode until the learn cycle recalibrates the backup window against the new cell's actual capacity.

RAID controller staying in write-through mode after battery swap

Write-through mode after a cell swap is almost always a learn cycle that hasn't run yet — not a faulty battery. The controller will not switch back to write-back until it has completed a full charge-discharge assessment and confirmed the backup window meets its internal threshold. On Adaptec cards this cycle can take 24–72 hours under normal server load. Check status with StorCLI /cx bbu show and confirm the learn cycle state shows "Active" or "Complete" before assuming the cell is defective.

Backup window estimate shorter than expected after new cell install

A shorter-than-expected backup window on the first assessment is normal — the controller's algorithm starts conservative when it has no history with the new cell. Capacity characterisation improves over two to three full learn cycles as the BMS builds an accurate discharge curve. The reported backup window will extend after each completed cycle until it stabilises. If the window remains below 72 hours after three cycles, check that the cell resting voltage is reading at or above 3.6V in the management interface.