with mine keep a 1000cca battery with a isolator off the main battery. I can run it into the ground and the vehicle still goes. when I'm on site I plug the van in and it switches straight to mains and shuts the inverter down. remove power and it fires right up without a glitch.
hardware wise: 7 port usb hub HP 1200 laserjet printer,40gb hd, 4g RAM, 3g modem, keyboard and mouse. 3kw inverter
display wise 17" LG monitor. base machine is a acer laptop. OS is winXP - extra memory is for quicken - its a memory hog!
it will run 3 days before shutting down. I use it daily for invoicing and general internet when I need info quickly.. it is also networked back to the workshop SBS server (quickbooks sits on this.)
the whole lot in integrated in the floor of my van . (if someone knows how to empty a nokia N70 memory card without the lead I'll show you the pictures.)