HP 727258-B21 RAID Controller Backup Battery 7.2V 1000mAh

HP 96W Smart Storage Megacel — 7.2V Li-ion Replacement Battery (727258-B21)

This 7.2V 1000mAh Li-ion cell replaces the backup battery on HP's Smart Storage Megacel RAID controller. It protects cached write data during power loss by giving the controller enough energy to flush its cache to disk. Compatible across the 96W Megacel and a wide range of HP ProLiant Gen9 servers, including the DL20, DL60, DL80, and 27 additional platforms.

• Gen9 ProLiant controller compatibility: These servers all use the same 96W Smart Storage controller board, sharing a common 7.2V battery connector and the same BMS handshake protocol — so one cell covers the full platform range without firmware changes.
• Bench tested on actual hardware: We cycled this cell through full charge, simulated power-cut events, and confirmed the BMS registered a valid backup window on the controller. The cell responded correctly to the learn cycle and exited write-through mode as expected.
• Post-installation learn cycle: After fitting, initiate a battery learn cycle from the controller management interface — StorCLI: storecli /cx bbu show, or ONTAP: system controller battery show. The controller holds write-through mode until the learn cycle finishes and recalibrates the backup window against the new cell. Skipping this step leaves write-back caching disabled indefinitely.

RAID controller staying in write-through mode after battery swap

Swapping the physical cell does not automatically restore write-back mode. The controller must complete a learn cycle — a full discharge and recharge sequence — before it recalculates the backup window for the new cell. Until that cycle completes, the controller treats the battery as unqualified and keeps caching in write-through mode, which reduces write performance significantly. Trigger the cycle manually via StorCLI or iLO as soon as the battery is fitted; it typically takes 24–72 hours under normal server load.

Management console showing a battery error days after installation

HP's controller does not run a battery health assessment at boot — it runs on a timed internal schedule, typically 24 to 90 days after the last completed assessment. If the previous battery had already passed its last assessment checkpoint, the new cell will not be evaluated until that interval expires. The error flag from the degraded old cell can persist in the console until the next scheduled assessment runs and passes. Check the assessment timestamp in iLO under Smart Storage Administrator and manually trigger a recondition cycle to clear the flag immediately.