Hitachi NAS Platform 4000 Series Hardware Reference Manual page 39

A replacement battery pack may not be fully charged (it may not be at 100% capacity)
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when it is installed. After a new battery pack is installed, the server performs tests
and starts a conditioning cycle, which may take up to 24 hours. During the
conditioning cycle, the full NVRAM content backup protection time of 72 hours cannot
be guaranteed.
If a server is left powered off, the battery will discharge slowly. This means that, when
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the server is powered up, the battery will take up to a certain number of hours to
reach full capacity and the time depends upon whether a conditioning cycle is started.
The scenarios are:
24 hours if a conditioning cycle is started
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3 hours if a conditioning cycle is not started
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During the time it takes for the battery pack to become fully charged, the full 72 hours
of NVRAM content protection cannot be guaranteed. The actual amount of time that
the NVRAM content is protected depends on the charge level of the battery pack.
A battery pack may become fully discharged because of improper shutdown, a power
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outage that lasts longer than 72 hours, or if a server is left unpowered for a long
period of time.
If the battery pack is fully discharged:
The battery pack may permanently lose some long term capacity.
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Assuming a battery conditioning cycle is not started, a fully discharged battery
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pack takes up to 3 hours before it is fully charged. If a battery conditioning cycle is
started, a fully discharged battery pack takes up to 24 hours before it is fully
charged.
A battery conditioning cycle is started if the server is powered down for longer
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than three months.
Chapter 4: Hitachi NAS Platform server components
Hitachi NAS Platform and Hitachi Unified Storage Series 4000 Hardware Reference
NVRAM backup battery pack
39