Does an alternator going bad kill a battery?

I was on vacation this week and the alternator died on my 03 Tribute. I was on a bridge and had to keep the car running to get off the bridge. As a result I drained the battery. I got towed to a dealer which quoted me $275 for a new alternator. I come back later and there is a bill for $850. They said anytime you run down the battery like I did it destroys the battery which was another $125. Then there was another $450 in labor and shop fees. I got them to give me the old battery (just a year old) which they were reluctant to do. Does running down a battery destroy it?

All batteries have what is called a reserve capacity. This is the amount of time the battery can continue to operate the electricals of the vehicle in the event the charging system fails, and is reflected in minutes. If the battery has a reserve capacity of 90, that means the battery will allow the vehicle to operate for 90 minutes without the charging system. So check the reserve capacity of your old battery to the amount of time you ran with the failed alternator.

But to be honest, when you use the reserve capacity of a battery, it shortens the battery’s life.


Doesn’t help it but repeated complete draining will reduce your batterys performance.Will it not be able to provide the energy to start your car NO,it just wont meet the specs but plenty of batterys that are being driven around now don’t meet the specs. printed on their cases.

Then again I wasn’t there,I did not test your battery,I did not see it fail too start your car,I did not see it refuse to accept a charge so I can’t say for sure you were ripped off and I don’t call people thieves without absolute proof.

It does sound like your car was running on just battery power longer than just the distance to get it off a bridge (this much battery only driving would not totally discharge a battery) because of this “hole” in your story you have no credibility,sorry that is how the facts line up.

I must correct myself,I did not consider if it was a 20 mile bridge that took you 2hrs to get off but then you did not offer this info. If this was the case I restore your credibility and apologize.

You need to consider that the failure of your alternator may not have been an all-at-once situation. If the alternator was failing over a period of days–which is typical–then the battery was being deeply discharged over an extended period of time, without sufficient recharging ever taking place. Then when you had to run the car on just the battery’s power in order to get off the bridge, that was the Coup de Grace, so to speak.

Not only is this scenario possible, it is likely.

If an alternator goes bad, it certainly can kill a battery. Car batteries don’t like being run all the way down. If you have a fairly new battery, you can usually get away with it once, maybe twice. If the alternator was ailing for a while, the battery may have been low for a long time, which also isn’t good for a battery. Fully charge the old battery and have it load-tested. If it performs well, get it in writing and challenge the shop that did the work. $450 in labor to change an alternator? Wow. Did they go through the tailpipe to change it?

You have a right to be pi##ed about this! It sounds like the dealer saw a money-making opportunity at your expense and took it.

Over the 60 years of my driving, I have had a few run-down batteries, but most of them recovered. I doubt that your battery was ruined.

Running down a battery compromises it. How much depends on its condition prior to running it down and how long and much it was run down.

They were not out of line in changing but it should have proposed to you unless you signed off on the car to what they please.

$850 was a ridiculous overcharge for this repair…Did this occur at night with the headlights on? Even so, the battery should have powered your car for at least a half hour…Have your old battery charged and then tested. That’s the ONLY way to determine if it’s serviceable…Then price a rebuilt alternator at a local parts store to see how badly they reamed you…

The service departments at new car dealerships should be avoided like the plague once the vehicle is out of warranty…

Usually, a sound 1 year old car battery can withstand a “deep cycle” or two without suffering major damage.

If your battery is 3, 4, or 5 years old a complete discharge might be the final straw. I’d still recharge it to see if it holds a charge OK. A 1 year old battery shouldn’t be killed off by one incidence of total discharage. Put a charger on your old battery, after it is charged you can take it to AutoZone for a “load test”.

To kill a relatively new battery it would need to be completely discharged and remain discharged for a period of a month ot so. A discharged battery that is not recharged fairly quickly can go bad due to remaining in the discharged state.

My guess is your battery is still an OK battery.

I fear they say those out of state plates and say dollar signs.

Do you guys see this thread is from June 09? Elly pulled it out of the archives for who knows what reason,definitely not for the OP’s benifit

Interesting. Good catch Oldschool. The OP probably doesn’t use this site anymore. Before your post, I was going to mention something that I noticed. It seems like most of the replies are implying that the alternator might have quit working, producing zero amps so the battery just died a natural death from being run down. I have another potential theory: What if the alternator regulator went out, allowing higher than 14.7 volts (but not high enough to burn out many light bulb), or continued to put out 14.7 volts, but did not taper off as should have when the battery got fully charged, and instead over charged the battary, heating up the plates and causing at least one of them to warp and short out. This might explain the battery “going out” at least that’s one way to explain the alternator making the battery go out. I will agree the labor charge and shop fees do seem rather steep. But that’s not worth discussing since this is an old post.

I just went to mavis for a new alternator, battery, and oil change @ $540. Yes. They ripped you off.

Well who ever was ripped off back in 2009 has probably gotten over it by now.

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Ahem . . .

OP hasn’t even returned to this website since 2009, so you’re pretty much talking to a wall

And you don’t even mention what kind of vehicle YOU have. So it isn’t even a valid comparison, without some more pertinent information

There’s a good chance OP doesn’t even have this vehicle anymore

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