There are three possible VBAT voltage low events. They are
VBAT lower non-critical, VBAT lower critical and VBAT lower non-recoverable.
"VBAT lower non-critical" is a warning event
and can be ignored.
when "VBAT lower critical" or "VBAT lower
non-recoverable" events are triggered, RTC battery should be replaced.
The VBAT thresholds can be found in IPMI web UI sensor readings
or run "ipmitool sensor".
From X11 platform, VBAT sensor type has been changed and
the status are "presence detected", "low" and "failed".
When VBAT status becomes "low" or "failed", the RTC battery
should be replaced. | 
