How to fully discharge a laptop battery

1) Restart the laptop.
2) When the screen shows first signs of life slowly tap the 'Del' key.
3) You should find the computer has booted into what's called the BIOS screen. This mode does not let your operating system (windows, linux etc) prematurely shutdown the system. If just left in this screen the battery will flatten completely.

* If 2) fails to deliver the BIOS screen try using the 'F2' key instead.
* If you intend to flatten the battery to prevent a 'memory' check the battery type before bothering (details are printed on the battery itself) A Li-ion battery will not develop a memory and any issues with these sorts of batteries are usually related to the connectors or old age.