How Do I Know If I Have A Bad Alternator?

The best way to check alternator to see if its charging is while the engine is running disconnect hot post battery cable from battery,if engine shuts down alternator is not charging the battery.

If it is your battery autozone and oriel's test for free they do the alternator too but I think you have to take it off the car before they test it an easier way some one informed me was that if you can start the car and remove the battery cables and it stays started than your alternator is good because that is what keeps the car running

Remove the battery terminals and if the vehicle shuts off, your alternator is most likely bad, remove it and take it to a place that rebuilds alternators and they will test it for you, as well they rebuild them as well... Cheaper than buying a new one and just as good.

When it finally turns does it start? If so it doesn't sound like an alternator to me. Sounds like a weak starter or possibly bendix. Depending the age of the vehicle, there might be other electronic devices involved.

If the alternator is bad, the battery light should be on or the battery gauge will show discharge. You will be running on the battery instead of the alternator. The will soon discharge totally and the car will cease to run.

More often the problem is your battery. Call around to car battery stores and find one that has a tester. They can test it in a few minutes and it is much less expensive to replace than the alternator.