When it comes to Lithium Ion cells, they are charge protected. In stalling the system and ripping out the AC adapter CE couldn't send the 'Critical battery level turn off immediatly' command.
You could have causes a surge which prevented the power out for occuring naturally. So do be careful, as Lithium Ion batteries with broken charge circuits can explode in extreamly nasty ways.
Guide to battery best use:
http://www.hpcfactor.com/support/cesd/h/0015.asp