When the critical percentage is reached Windows does shut down but not cleanly. Server 2008 and Vista both do the same thing...they simply power off without shutting down normally. In event viewer you will notice an unexpected shutdown error has been logged.Vista was tested on a laptop and Server 2008 was tested with a USB connected APC UPS.Just set the critical and low actions to a higher percentage...no sense waiting hours for batteries to drain.UPDATE: I know ACPI is working properly because pressing the power button on both machines shuts down windows properly.

Hi,This is a known issue with Vista/Windows Server 2008. If you set Critical Battery Action to Shut Down, it will not work properly to shut down system. Error 6008 was recorded in Event log. Product Team has investigated this issue. But solution is not available currently due to the complexity of involved system components. This should be fixed in further release. Sorry for the inconvenience this has brought.I suggest you change the Critical Battery Action to Sleep or Hibernate to avoid unexpected shut down.Thanks.

Is there a patch yet ? Running Server 2008 and I do not want to try another UPSshutdown test until patch applied.Thanks,Ralph

I would also like to know. It has been more than a year since this post was made.