Here is an article that describes why you should never try to remove a battery cable when the engine is running. I can't tell you how many vehicles I've repaired because of that. Computers and alternators fry pretty easily.

Sometimes people get lucky, but about half the time they don't. Don't do it. the charging system is just too lucky to diagnose; no need to do this!!!

http://www.troubleshooters.com/dont_...ct_battery.htm

 

I agree ^ I got lucky use a multi meter and test it the right way