I am trying to drain the battery of a Nikon D7000. A general technique is to leave it on slideshow mode for several hours, but unfortunately the display turns off automatically after just a few minutes. I've searched the entire internet but it seems all the threads have to do with fixing the problem of unwanted battery drain, as opposed to intentionally draining the battery.
There should be a setting to disable the auto sleep function of the camera. With this you can then leave the playback image mode on.
If the camera has a Liveview mode you could turn that on as it would probably drain battery more quickly, but be cautious with this because it means leaving the sensor exposed. You could reduce this by ensuring that a lens is fitted to the body, and minimise risk of damazing the sensor with light by leaving the lens cap on.
All this said, wanting to drain the battery is unusual, and do a search for the properties of the battery type you are trying to drain (eg lithium ion Li-ion or nickel metal hydride nimh) as their characteristics may mean that draining the battery completely may cause damage to it
Draining (or calibrating - initialising) the battery without a proper charger is not possible. Like you said, at a certain level, everything shuts down. To drain the battery completely, you have to continue using power. The only thing thats still alive is the top display. If you switch on the light of the top display (by turning the on/off switch one notch further), the battery runs out eventually. Repeat a couple of times and your battery is initialised