My daughter's 2006 Scion has intermittent charging problems. The car is having problems staying running and not starting and we have to rev it up to keep it from dying. Autozone tested the system and said the battery was bad so she got a new battery, the problem stopped for a week then again same problems. I took off the positive battery cable and it died, then they tested it and said alternator was bad so I changed it out. The problem stopped for several months and then it happened again, they tested and said alternator had failed so a friend changed the alternator and it lasted a few months and now we are having the same problems. Yesterday they told my daughter everything was working normal, I took the car in a few hours later when it was running poorly and they said battery was bad so we changed it since it was under warranty then they said the alternator was bad. Now, today its starting and running fine. They are willing to give the money back so we can purchase a factory alternator but at this point I don't think its the alternator or battery, there seams to be another problem, any help would be appreciated. Thanks
Never, never take the battery cable off when the engine is running. The voltage surges are death for computers.
Overcharging is the cause for the battery failing and also the alternator. A factory replacement is most likely the answer along with a new battery. Then monitor voltage at the battery. It should be 14 to 14.5 volts