IBM ServeRAID-8s RAID Controller Replacement Battery 3.7V 1800mAh

IBM ServeRAID-8s / ServeRAID-8i — 3.7V Li-ion Replacement Battery (39R8812)

This is a 3.7V, 1800mAh Li-ion backup cell for the IBM ServeRAID-8s and ServeRAID-8i RAID controllers. It backs up the controller's write cache during a power loss, holding data long enough for the controller to flush it safely to disk. Fits models including 13N2233 and ServeRAID 8i SAS; also cross-references OEM part numbers 25R8118, 39R8731, and 13N2256.

• ServeRAID-8s and 8i platform: Both controllers share the same battery form factor, connector pinout, and BMS handshake protocol. The controller firmware validates cell voltage and internal resistance at boot before enabling write-back mode.
• Bench tested on actual hardware: We ran charge-discharge cycles against the BMS and confirmed the cell communicates correctly with the controller. The battery passed OCV checks at 3.7V nominal and the BMS reported no fault flags during load simulation.
• Learn cycle after installation: After swapping this cell in, trigger the battery learn cycle from your controller management interface — StorCLI: /cx bbu start learn; ONTAP: system controller battery show. The controller will stay in write-through mode until the learn cycle completes and recalibrates the backup window estimate against the new cell. This takes 24–72 hours under normal server load.

ServeRAID-8s staying in write-through mode after battery swap

The controller does not automatically switch back to write-back mode when a new battery is installed. It stays in write-through mode until it completes a full learn cycle and confirms the backup window meets the minimum threshold — typically around 72 hours. Until the learn cycle finishes, write performance will be noticeably lower because every write goes directly to disk with no cache buffering. Kick off the learn cycle manually via StorCLI or the IBM ServerGuide interface immediately after installation to start the clock.

Management console still showing a battery error two days after installation

IBM's ServeRAID battery self-assessment runs on a scheduled interval, not at the moment the controller detects a new cell. If the last assessment ran before the swap, the console will continue to report the old error until the next scheduled test executes. The assessment cycle is typically set to 30 days by default, so the error can persist well past installation day. Force an immediate reassessment by running /cx bbu start learn in StorCLI — once the cycle completes and the backup window is validated, the error clears.