Battery Question?

If you have a bad battery, will your car run rough? Also will the engine seem louder? Can the alternator run while your car is on? If so, what would it sound like?

Low voltage can cause a car to run rough especially if the alternator is not working. The alternator will only produce voltage when the engine is running. Usually a properly working alternator is quite in operation however sometimes there may be a slight whine to the alternator but not very often. I doubt it very seriously if the car would sound louder due to a bad battery but if it is running rough it may due to the engine misfiring.

Can you hear the alternator? What does it sound like?

What makes you think your engine running rough is because of a bad battery for starters? But yes a bad battery can make your engine run rough but it's rare and you'll only notice it if you can get your car started cuse a bad battery won't start a car.

Well, it starts, but i went and had it tested and the test said it was a bad battery. So we are going to get it replaced. But there is a noise, i dont know how to describe it, but, its coming from the passenger side under the hood. what could be?

How old is the car? Battery should last around 3-4 years at least. Even if it fails before 3 or 4 years, the battery is either replaced FREE or pro-rated.

Bad battery will make the alternator work harder to compensate for a failing battery over time with this condition, it will also kill the alternator.

If you can bring the car to Autozone, I think they can install your battery for FREE and probably they can tell you where and what the sound is and what part it could be.

Your car starts but someplace test you and says your battery is bad, let me guess they want to sell you a new battery ASAP. Not to question their fine morality and expertise but how can a working battery be bad. If it didn't start or had a hard time starting (cranked over slower than usual) in cold weather but worked good in warm weather sure the battery could be bad. Basically if you never have a problem starting the car then your battery is in fine working condition, I'm from the school of "If it ain't broken don't fix it." Maybe they went to the school of "Let milk them fools (wallets)" who knows.

As for alternator sounds, you shouldn't hear it if you do it's either new and the bearings have yet to wear-in or it's old and the bearings or something internal have worn/broken. A new alternator will typically whine a bit but over time it'll stop, an old alternator will whine, grind, knock, or make no unusual noise at all it all depends on what breaks but it'll always come from the alternator.

You should track down the sound by starting the car and then listen around under the hood to track down the source of the sound.