i have a 99 ford f150 v8 triton, and it has 80,000 miles on it, and recently i was driving and everything electrical went out, but was still running, i took the battery up to get it tested and they said it had a bad cell in it, so i got antoher one, and a day later it did the same thing, could it be a bad alternator, or just a bad battery?? please help

 

What do you mean by "everything electrical went out, but was still running"?
The engine would not continue to run without electrical power to the fuel pump, engine control module (etc..) Did you just loose the cluster display and radio?

The battery light will come on in the cluster if the alternator is not outputing while the engine is running.

 

thanks, it was the alternator!