IBM AS400 iSeries 2757 RAID Controller Compatible Battery 3.7V

IBM AS400 iSeries 2757 — 3.7V Li-ion Replacement Battery (53P0941)

This 3.7V, 3400mAh Li-ion cell replaces the OEM battery on the IBM AS400 iSeries 2757 RAID controller. It backs the controller's cache memory during power loss, keeping pending write operations safe until power is restored. Fits controllers using OEM part number 53P0941.

• AS400 iSeries 2757 RAID controller fit: The 2757 controller uses a dedicated lithium cell to hold volatile cache data during unexpected power failures. The BMS on this card checks cell voltage and internal resistance at initialisation — a cell outside spec triggers write-through mode immediately and holds it there.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge under a controlled load matching the controller's float current draw. The BMS accepted the cell without error, and voltage held stable across the test window with no mid-cycle cutoff events.
• Learn cycle after installation: After swapping the battery, trigger a learn cycle from the controller management interface — on ONTAP use system controller battery show, on Broadcom/LSI use StorCLI /cx bbu show. The controller will not return to write-back mode until the learn cycle completes and recalibrates the backup window estimate against the new cell's actual capacity.

RAID controller staying in write-through mode after battery swap

Swapping the battery does not automatically return the controller to write-back mode. The 2757 controller recalibrates its backup window estimate only after a full learn cycle completes — this process measures how long the new cell can sustain cache voltage under the actual load of that specific controller. Until that cycle finishes, the controller treats the backup window as unknown and defaults to write-through as a precaution. Depending on server load and ambient temperature, the learn cycle typically takes 24 to 72 hours. Confirm completion by checking battery status — the controller returns to write-back mode once the backup window reads a confirmed positive value.

Management console reporting battery fault days after a confirmed successful install

This happens because the controller's battery health assessment runs on a timed interval, not at the moment of installation. If the scheduled self-test fires before the learn cycle has fully completed, the controller logs a fault because it cannot yet confirm a valid backup window — the cell voltage is within range, but the backup window estimate is still being calculated. The fault clears once the learn cycle finishes and the next scheduled assessment reads a confirmed value. If the fault persists beyond 72 hours post-installation, check cell voltage directly via StorCLI — it should read between 3.6V and 4.2V at rest.