The e780 detailed spec sheet is online; I guess the author didn't look for it.
http://sp.ts.fujitsu.com/dmsp/docs/ds-lifebook-e780.pdf
The 18-hour battery life comes from the combination of an 83 watt-hour battery (8 cells) and a 41 watt-hour battery (four cells). That all works out to an average power consumption of about 6.9 watts, which is unusually low for a full-size laptop but within reach of modern chipsets. The 18-hour figure is based on testing with MobileMark 2007, which means the laptop is doing almost no work at all beyond just staying awake and moving small amounts of data around. The network doesn't even have to be connected. You should expect to get more like 9 to 12 hours of real-world operation, which is still very good. The machine probably weighs seven to eight pounds in this configuration, so that's something to think about.