Automotive

Driving with a dead battery bad?

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  • Jan 20th, 2014 4:08 pm
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[OP]
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Jun 28, 2012
5562 posts
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Calgary

Driving with a dead battery bad?

My battery died tonight and had to have the car boosted. The only place open at the time and closest was walmart which was 10mins away. I really was not sure about driving my car to walmart (even only 10mins), with a dead battery and all the extra charging responsbility on the alternator (which the alternator is not designed to do). But I had no choice cause the person who boosted my car, had to go somewhere after and was willing to follow behind me on the way to walmart (in case i stalled), but wasnt willing to drive me there to get the battery and back to my place while leaving my car at home cause they were heading in the other direction. In total I had the car running for 15mins tops. My biggest worry is that driving with a shorted/dead battery was bad for alt. I could hear whine from my alternator, which i never get. But once i put the new battery in, it was gone and back to normal.

You think this put a lot of strain or damage on my alt? I tried to make it to walmart as fast as i could to shorten the trip. i just hope i didnt damage the alt or shorten its life.
17 replies
Deal Expert
Jan 15, 2006
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Richmond Hill
It's over...going to blow up soon.
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Apr 14, 2004
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Toronto
The battery completes the electrical circuit in a car so driving with a bad battery is not recommended.
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Jul 21, 2011
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RMB
EP32k2 wrote: It's over...going to blow up soon.
oh no is gonnna blow, so scary :-0
Sr. Member
Dec 16, 2008
987 posts
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Richmond Hill
Your alternator will be the next one to die.
Deal Addict
Sep 30, 2008
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your car alternator should have suffered no harm whether charging a dead or good battery.
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May 10, 2005
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Ottawa
If you can get your car started, then there is no problems with driving it to the nearest place to get it replaced. the only concern would be keeping the revs up so the car does not stall. If it should stall, you may not have enough juice in the batter to re-start your engine.
To answer your question, no, it is not harmful to drive the car, it will not "strain" your alternator or cause it any harm at all.
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Apr 20, 2011
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ON
I stupidly forgot something plugged in the accessory socket a couple summers ago while on vacation. Was away all day and returned to dead car (not even power for remote lock)
Fortunately a kind stranger gave me a boost in the parking lot. I drove for 30-45 mins straight on the hwy and good as new. My alternator is fine and that same battery is still working in my car. Granted, it struggles a bit on very cold days, but it's also coming up on 9 years, so that's too be expected.

TLDR; unless this is a regular habit, your alternator will be just fine.
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May 10, 2005
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aqnd wrote: I stupidly forgot something plugged in the accessory socket a couple summers ago while on vacation. Was away all day and returned to dead car (not even power for remote lock)
Fortunately a kind stranger gave me a boost in the parking lot. I drove for 30-45 mins straight on the hwy and good as new. My alternator is fine and that same battery is still working in my car. Granted, it struggles a bit on very cold days, but it's also coming up on 9 years, so that's too be expected.

TLDR; unless this is a regular habit, your alternator will be just fine.
A drained batter can be charged by the alternator, as it is supposed to.
A dead battery, for whatever reason, may not be chargeable and therefore your ignition and accessories would be running on the power delivered by the alternator alone. This could lead to the alternator being overloaded. Short drives are OK but long ones (like yours) could cause damage to the alternator.
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Apr 20, 2011
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Technically an alternator is supposed to top up a mostly-charged battery
A battery that holds no capacity means the alternator is running at max, the same as a 'healthy', but dead battery would. The alternator doesn't know what is wrong, just that it needs to keep at max to maintain voltage. 15 mins at max is 15 mins at max in either scenario, not easy on alternator, but it should survive just fine

It may actually be easier in his case.
E.g.
Scenario A - battery 0% - alternator has to run at max to run the vehicle load AND charge battery at the same time
Scenario B - battery 0%, but does not accept charge - alternator is not necessarily at max, it just has to maintain the vehicle load, as the battery is not drawing current as it is unable to charge.

In scenario A, the output drops as the battery charges, but there's still the draw of the vehicle systems to overcome
Sr. Member
Dec 24, 2013
668 posts
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Toronto
Mayosandwich wrote: My battery died tonight and had to have the car boosted. The only place open at the time and closest was walmart which was 10mins away. I really was not sure about driving my car to walmart (even only 10mins), with a dead battery and all the extra charging responsbility on the alternator (which the alternator is not designed to do). But I had no choice cause the person who boosted my car, had to go somewhere after and was willing to follow behind me on the way to walmart (in case i stalled), but wasnt willing to drive me there to get the battery and back to my place while leaving my car at home cause they were heading in the other direction. In total I had the car running for 15mins tops. My biggest worry is that driving with a shorted/dead battery was bad for alt. I could hear whine from my alternator, which i never get. But once i put the new battery in, it was gone and back to normal.

You think this put a lot of strain or damage on my alt? I tried to make it to walmart as fast as i could to shorten the trip. i just hope i didnt damage the alt or shorten its life.
The dead battery probably was drawing max. current from the alternator at the time. Doubtful there would be any permanent damage for such a short trip. You would have been better off boosting the car, then disconnecting the battery, and then drive to where you need to go.

OR

grab a cab. =/
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Mar 18, 2004
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Mayosandwich wrote: with a dead battery and all the extra charging responsbility on the alternator (which the alternator is not designed to do).
So what is your alternator designed to do? Does it act as a counter weight to the engine to add better corning capabilities?
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Sep 3, 2005
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Vaughan
If the battery was indeed dead, and not just drained. You should have just changed the battery in the walmart parking lot.

I've changed a few batteries in parking lots. It takes a few mins. I've changed them in cold weather (winter time) as well.
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Newbie
Feb 26, 2013
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Your car's dead battery can damage the alternator beyond function/repair. So, you must get the new battery as soon as possible.
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Feb 9, 2003
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Langley
A dead battery still has 10-11 volts on it. If it was truly completely flat, you wouldn't have been able to start your car until the other car charged it up somewhat. With a voltage drop of only a couple volts, it's not too much work for the alternator. And even if it was, limiting current output is one of the things that the alternator regulator was designed to do.
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Nov 10, 2004
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i don't know about cars but i've seen a friend changed his car battery while the car is running (after he jump started the car). =p he said something about preventing the ECU from resting itself.
Sr. Member
Sep 18, 2004
563 posts
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So much misinformation here, and information that is so pedantic and dealing with unlikely cases, that it borders on misinformation.

OP, your alternator will be fine. If it dies as a result of this drive, it was a bad alternator already, and maybe the extra load contributed to its demise a little sooner. But it's very unlikely that you'll see any effects.
Newbie
Jul 25, 2019
1 posts
Hi so my battery on my 2016 toyota corolla is dying, it will still start up but sometimes it has trouble getting started. My uncle can out a new battery in for me, He's a mechanic, but he lives 3 hours away and I'm scared I'm going to get stranded on the freeway. Do you think its okay to make it over there?

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