I am an EE with a background in power systems engineering, and I call NOT BS on what pantera said. The lithium-ion battery chemistry does not take abuse (overloading, overdischarge, under-voltage, charging too fast, out of temperature bounds) very well. These conditions damage the cell, and the battery fails quite violently. The protection circuitry is there to turn off the battery if it notices the conditions before damage occurs. With a cheap battery, I would not be surprised that the protection circuitry is the first thing they cheap out on.