Nexergy NEX900803 RAID Controller Compatible Battery 7.2V 3400mAh

Nexergy NEX900803 / FAS2240 RAID Controller — 7.2V Li-ion Replacement Battery (271-00025)

This 7.2V 3400mAh Li-ion battery replaces the backup cache battery in Nexergy RAID controllers including the NEX900803, NEX-900803, 2040, and FAS2240 series. It maintains volatile write-cache data during a power loss event, protecting against data corruption while the controller waits for power to restore. OEM part numbers covered: 271-00025, 271-00029, and 271-00024.

• NEX900803 / FAS2240 compatibility: These controllers share the same 7.2V battery rail, connector pinout, and BMS handshake protocol. Swapping within this group does not require firmware changes — the controller reads cell chemistry and voltage range directly from the BMS on first boot.
• Bench tested on actual hardware: We ran this cell through a full charge and BMS initialisation sequence. The protection circuit triggered correctly at both low-voltage cutoff and over-temperature thresholds. The cell held charge across repeated discharge cycles without BMS fault flags.
• Post-install learn cycle — do not skip it: After fitting this battery, initiate the learn cycle from your controller's management interface. In ONTAP, run system controller battery show. For Broadcom/LSI controllers, use StorCLI /cx bbu show. The controller stays in write-through mode until the learn cycle recalibrates the backup window estimate against the new cell's actual capacity.

RAID controller staying in write-through mode after battery swap

Write-through mode means the controller is not using write-back caching — every write goes directly to disk, which slows I/O significantly. This happens because the controller has not yet verified the new battery can sustain the backup window required by its policy. It will not automatically switch back to write-back mode until the learn cycle completes, which can take 24 to 72 hours under normal load. Force the cycle manually via ONTAP or StorCLI rather than waiting for the scheduled trigger.

Management console showing a battery error days after a clean installation

The controller does not assess battery health at the moment of installation — it runs a scheduled self-test on a timed interval, often 24 to 90 days depending on firmware version. If that test fires before the learn cycle finishes, the controller flags the battery as unverified and logs an error. This is not a fault with the cell itself. Trigger a manual learn cycle immediately after installation so the scheduled test finds a fully calibrated battery rather than an uninitialised one.