Honda Civic Owner's Manual page 76

Gauges
Charge/Assist Gauge
IMA ASSIST GAUGE
IMA CHARGE GAUGE
This gauge shows you the status of
the Integrated Motor Assist (IMA).
When the IMA battery is being
charged, the bottom side of the
gauge illuminates. When the IMA is
assisting the engine, the upper side
of the gauge illuminates.
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If the IMA battery is too hot or too
cold, the IMA system limits the IMA
battery's output power to protect the
battery. This disables the IMA assist
and Auto Idle Stop, even though the
Battery Level Gauge may show that
the battery is well-charged.
Therefore, if the motor assist is
frequently used, the battery
becomes hot and starts to limit its
output power.
It takes the IMA system a few
minutes in cold weather to normalize
the IMA battery's output power, and
about 15 minutes in hot weather.