[Andy]

Ever heard of this one? I just replaced my wife's car battery (purchased in 2003 so didn't feel so bad) and the battery guy said to extend the life of a car battery, you should turn everything off (radio, AC, etc) before you turn off the car!!

 

[Relayer]

I started doing this when I bought my last new battery. It just seemed to make sense that it might be helpful not to have all the accessories firing up and pulling on the battery when cranking up on my next trip.

 

[Jovan]

Thanks! My battery's been going kaput and I had to replace it recently. After lots of sweat, language that would make the late George Carlin blush, and a routine damning of the designers who made it so only a Chevy dealership could get to the battery, I now have something reliable under the hood.

Oh yeah, and I replaced it in a parking lot. At 2:00 in the morning.

So, anything that will extend the life of this one will be greeeat.

 

[PedanticTurkey]

Ever heard of this one? I just replaced my wife's car battery (purchased in 2003 so didn't feel so bad) and the battery guy said to extend the life of a car battery, you should turn everything off (radio, AC, etc) before you turn off the car!!

He's probably right, because the battery will get taxed when you start the car with all those things on.

The trick to keeping your battery in good shape, by the way, is not to discharge it completely. A full drain once can ruin a battery.

 

[Stringfellow]

The radio doesn't matter so much, but having the A/C off is important. It requires a lot of power to start a car engine and the engine drives the A/C - the A/C is not electrical but mechanical. Always turn your A/C off before you turn the car off. Your battery, alternator, and especially your starter will thank you.

 

[Asterix]

The radio doesn't matter so much, but having the A/C off is important. It requires a lot of power to start a car engine and the engine drives the A/C - the A/C is not electrical but mechanical. Always turn your A/C off before you turn the car off. Your battery, alternator, and especially your starter will thank you.

Thanks for the tip.

 

[Andy]

I guess we learned something today!! And my wife's battery is still working!! :icon_smile:

But now I'm going to have to remember something else when I turn off the car!

 

[Mike Petrik]

Not so fast ...

Based on my recollection from the Car Talk guys, this used to be true but is no longer true with today's cars, which have an auto-delay on accessories so that they turn on instantly AFTER the car is started. In other words they do not drain the battery but work off the alternator. It is true of older cars though.

 

[chatsworth osborne jr.]

Pfft, I never use AC

Next time you start a car, have everything on. If you pay attention, you'll hear the radio cut out for a split second and see the headlights dim.

I've been told this is because these items switch off to deliver full cranking amperage from the battery, not because of excess draw. I'd hope it is the same with cars. A belt-driven AC compressor could cause extra drag, but I really am not sure how that engages.

If the vehicle is not driven almost daily, a battery tender will prevent sulfation, but I doubt regular accessories will cause enough drain to do any damage. I mean winter starts are very hard on batteries (less available current, more required) and when is the last time a modern car didn't turn over when it was 20 degrees out?

 

[Beresford]

Based on my recollection from the Car Talk guys, this used to be true but is no longer true with today's cars, which have an auto-delay on accessories so that they turn on instantly AFTER the car is started. In other words they do not drain the battery but work off the alternator. It is true of older cars though.

Now there's a concept, a radio show combining Car Talk with Ask Andy About Clothes!

The first question could be about a mysterious car problem, the next could be on what is the precise date when it is proper to begin wearing seersucker, and so on. You could even have mixed questions, such as what types of caps is it sartorially proper to wear when you are driving a convertible roadster.

If Andy is as humorous as the Tappett Brothers, it could be a huge hit.

:icon_smile_big:

 

[Laxplayer]

Based on my recollection from the Car Talk guys, this used to be true but is no longer true with today's cars, which have an auto-delay on accessories so that they turn on instantly AFTER the car is started. In other words they do not drain the battery but work off the alternator. It is true of older cars though.

My mechanic told me the same thing.

 

[Mad Hatter]

The radio doesn't matter so much, but having the A/C off is important. It requires a lot of power to start a car engine and the engine drives the A/C - the A/C is not electrical but mechanical. Always turn your A/C off before you turn the car off. Your battery, alternator, and especially your starter will thank you.

True, but not for the reason of mechanical load-unless you're talking about something pretty old.

An air conditioning compressor is mechanically-driven, but they have an electric clutch. If the A/C is off, there is no load when starting. The compressor sheave is freewheeling.

Additionally, the blower motor is drawing current. On the highest setting there is sufficient draw that high-speed on a blower is usually on a seperate circuit and through a relay.

 

[JAGMAJ]

True, but not for the reason of mechanical load-unless you're talking about something pretty old.

An air conditioning compressor is mechanically-driven, but they have an electric clutch. If the A/C is off, there is no load when starting. The compressor sheave is freewheeling.

Additionally, the blower motor is drawing current. On the highest setting there is sufficient draw that high-speed on a blower is usually on a seperate circuit and through a relay.

I actually think you're both right. The A/C compressor will only be engaged if the A/C is on, but if it is on, it will cause a mechanical load on the engine as you go to start it. So, ultimately, the best thing is to turn off the A/C. As for the other accessories, I can't see there being much of an impact on the battery life, even if they are not automaticaly cut-off until the car is started.

 

[Mike Petrik]

I trust the Car Talk guys

--------------------------------------------------------------------------------

Dear Tom and Ray:

Please resolve an ongoing "discussion" in our home. Should the air conditioner be turned off when you shut off the engine? My theory is that if you turn off the a/c, when you start the car, it won't cause as much strain on the battery as this question is causing here at home. Thank you for resolving this. Bill

Tom: Do you like the taste of humble pie, Bill? I hope so.

Ray: You don't need to turn off the air conditioner. In fact, it doesn't make any difference. When you turn the key to the crank position, all of the major accessories are AUTOMATICALLY turned off while the car starts.

Tom: That allows all of the battery's power to be used for starting the car. Once the car is started, the a/c, the radio, and the hot plate all come back on.

Ray: So that settles it, Bill. And by the way, tell your wife we got the 20 bucks she sent in last week.

 

[Andy]

Mike:

That makes sense and those Car Talk guys know everything!!

 

[Mike Petrik]

Mike:

That makes sense and those Car Talk guys know everything!!

Everything about cars at least. These professors of the mechanical arts express political views that are more common with their NPR colleagues than their mechanic colleagues, but that certainly does not impair their authority in matters automotive.

 

[M6Classic]

Mike:

That makes sense and those Car Talk guys know everything!!

Tom and Ray used to maintain and repair my car. They were excellent, best mechanics with whom I have ever worked! Honest, too, and reasonably priced. I think Ray still runs the garage somewhere near Kendal Square in Cambridge, though I have moved on.

If you ever wander throough Harvard Square and get to the intersection of MassAve and JFK St. (Boylston St. to us old-timers), facing the Curious George book shop, look up and you will see the office windows for Dewey Cheatham & Howe.

Buzz

 

[jbmcb]

On a somewhat related note, the A/C compressor disengages whenever the engine is under heavy load, so when you have to floor it to get on the freeway, the A/C disengages momentarily to give the engine more power.

More and more accessories are being driven by electric motors these days, as they can be more efficiently controlled by the vehicles computer. So far the power steering, radiator fan, and, sometimes, the brake pumps are being driven by electric motors. Soon everything will be driven electrically, leading to better fuel economy overall.

 

[Zingari]

My father in law has my old Audi that still has the original battery on it from Jan 2001 - used daily for local travel without the application of special measures.

Seven years from a battery is good enough for me.

 

[Mike Petrik]

On a somewhat related note, the A/C compressor disengages whenever the engine is under heavy load, so when you have to floor it to get on the freeway, the A/C disengages momentarily to give the engine more power.

More and more accessories are being driven by electric motors these days, as they can be more efficiently controlled by the vehicles computer. So far the power steering, radiator fan, and, sometimes, the brake pumps are being driven by electric motors. Soon everything will be driven electrically, leading to better fuel economy overall.

Interesting, thanks.