it doesn't look good indeed, start with restarting the management agent of ESXi, if the error is still their download a Dell Diagnostic CD and see what happens...
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This is a normal behaivour for DELL Servers which have RAID Controllers with BBUs. All DELLs in our cluster do this once a week.
learning curve (Same like APC do from time to time)
If you check the OMSA at the same time you'll see a msg in the logs about this event.
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