I have a number of clients who are running VMWare ESXi 5.0 free edition servers, and they usually have some form of cheap UPS connected to the server.
The most common one is the CyberPower PureSinewave 1500VA UPS, which can power the server for about 10 minutes or so before it shuts down.
The UPS normally connects to the PC over USB. On a regular computer, this USB would appear like a laptop battery, and Windows can initiate a shutdown or standby just like a laptop does.
How can I get VMWare ESXi to standby the virtual machines and power off if the UPS goes onto battey power?