The source symptom strongly pointed at firmware-setting retention rather than ZimaOS itself: normal restart was fine, but after the power supply was disconnected for a longer period, the ZimaBlade forgot the saved boot order and returned to the wrong/non-UEFI boot choice. The user could manually restore the order and boot normally again.
More than a year later, the original poster returned with a confirmed resolution: they replaced the CMOS battery and reset BIOS, and said this solved their issue. They identified the ZimaBlade battery as CR927 and contrasted it with the ZimaBoard's CR2032. This is source user verification, not an IceWhale hardware service bulletin, so verify the battery physically before purchasing a replacement.
Cold Power Loss and Normal Restart Behaved Differently
The system kept its boot configuration through ordinary restart. The failure happened after shutdown plus extended PSU disconnection.
That pattern is classic evidence for settings not being retained while the board has no external power.
ZimaOS Requires UEFI Boot in the Current Installer
Current IceWhale installation documentation requires UEFI boot mode and Secure Boot disabled. If firmware falls back to a legacy/non-UEFI disk entry after CMOS settings are lost, ZimaOS may no longer boot even though the system disk itself is healthy.
Use the current ZimaOS boot requirements.
The Same Firmware Loss Also Affected Non-ZimaOS Boot Entries
Another source user had Proxmox installed on an SSD and found that removing power caused the board to fall back to default CasaOS/eMMC instead of the custom boot entry. That supports a firmware/NVRAM-retention layer rather than a ZimaOS filesystem bug.
The Source Fix Was Replace CMOS Battery, Then Reset BIOS
On March 10, 2026, R0GGER wrote that replacing the CMOS battery and resetting BIOS solved the problem.
This is much stronger than the earlier speculation that “the CMOS battery has no function” or that a BIOS update must be required.
The Source Says ZimaBlade Uses CR927
The OP later answered a battery-size question:
- ZimaBlade: CR927;
- ZimaBoard: CR2032.
Because this detail came from the forum user rather than a current IceWhale replacement manual, inspect your exact board/revision and connector before replacing anything.
Replace the Battery Only with Power Removed
Shut down cleanly, disconnect external power, avoid shorting the holder/board, and note the battery polarity/connector arrangement. After replacement, enter BIOS and restore the required settings deliberately.
Restore the Full Firmware Configuration, Not Only Boot Order
A dead/reset CMOS can also lose virtualization, SATA/controller, date/time, power-on, or other firmware settings. If you rely on VT-d, VM passthrough, auto-power-on, or a custom OS disk, verify those settings too.
ZimaBlade Boot Order FAQ
Did the original user confirm a fix?
Yes. Replacing the CMOS battery and resetting BIOS solved the issue for them.
Was a BIOS update confirmed as the fix?
No. It was discussed early, but the source-confirmed fix was the CMOS battery replacement/reset.
Which battery did the source user identify for ZimaBlade?
CR927. Verify your exact hardware before replacement because the detail is community-supplied.
