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I noticed the manual recommends NOT keeping you lights on auto if not driven for a week our more (Pg 71). I ask then what's the point? What is everyone else doing with their headlight setting? Can it really draw that much power when the car its off, and why would it anyway?

Ron
2012 CT EX-L w/o Nav

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Ours have been on since day one, no problems. It may just be one of those off liability entries that lawyers required them to put in there. It's also possible that it may have to do with some places having laws that say it's illegal to run fog lights when NOT in inclimate weather. Basically a way of suggesting you check on such things when you turn your lights on.

That far off, odd, abstract response was the best thing I could come up with in a matter of seconds, so I could be nowhere close to the right answer.
 

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I think this has to do with the capacity of the battery more than anything else. Let’s say you drive your vehicle to go to work on a cold wet late evening. You then have your lights on, seat heaters, rear defroster, heater, fog lights, wipers, and the many other electrical accessories also running. Well, it’s doubtful that the alternator can keep up with this electrical demand especially when you park the car and the lights stay on (AUTO) for an additional 15 seconds. That might be enough of a drain to prevent restarting.

In the owner’s manual page 100, it states: “Do not use the seat heater in the HI setting for an extended period, because it draws large amounts of current from the battery.” And then also: “If the engine is left idling for an extended period, do not use the seat heaters even on the LO setting. It can weaken the battery, causing hard starting.” Obviously because the alternator does not really have much output at idle.


On page 71 of the manual in discussing the AUTO feature of the headlights it uses the same verbiage as with the seat heaters being: “You should also turn off the lights if you plan to leave the engine idling or off for a long time.”

Looking in the manual on page 403, it states the wattage for the Low beam headlights as 55 watts. With the other lights, you are looking around another 20 or 25 watts. That’s a lot of wattage draining without the vehicle running. The manual lists the spec for the battery as 12v – 72 AH/20 HR.

Automotive batteries are not designed to be cycled (drained way down and then charged back up) like a deep cycle boating battery. This can easily shorten the life of the battery.
 

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use of battery

>>I think this has to do with the capacity of the battery more than anything else.<<

I'll yield to your superior knowledge... but I thought car batteries are used only for starting, not to provide reserve power while the engine and alternator are operating.

Years ago, when Chrysler introduced the alternator (replacing the DC generator), they ran a commercial that showed a car start, and then the battery was removed, and the car kept going and going and going.

Are things different now?
 

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Michael, first off, I don’t have superior knowledge or such. I’m often wrong. I don’t mind being proven wrong as it is a great learning experience.

In the attached picture you will see the amperage charging rate for an alternator. Notice that at low RPM’s of around 1000 to 1500 RPM there is minimal output from the alternator. The alternator doesn’t start kicking in strongly until around 2000 to 3000 RPM. Keeping in mind Ohms law of Watts = Volts x Amps. So if you have lights, seat heaters, rear defroster, fog lights, defogger, and more on, then you probably have a need of about 700 watts. Now 700 watts divided by 12 volts = 58 amps. As you see from the graph, to get 58 amps from your alternator you need to be around 3000 RPM. Well, what happens when you are just sitting there idling at 800 RPM and only putting out 8 or 10 amps? You start draining the battery! This is why on a cold morning when you go out to start the car, turn on all the accessories and then go back into the house for 15 or 20 minutes to finish breakfast and then come out to a vehicle that has stopped running with a dead battery.

As to your example of running a vehicle and pulling off the battery terminal, yes, as we now know your alternator will put out about 8 or 10 amps at idle. That is more than enough to run the electronic ignition, ECU, fuel injectors, and other small circuits that require the running of the vehicle. If Chrysler would have turned on the headlights or such in their demonstration, the car would have died quickly. If you can’t tell, I use to teach automotive at the local college.
 

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I've got another theory that I'll throw out there...

Since the headlights turn on for a few seconds every time you open the driver's door, this would inevitably drain the battery down at a much quicker rate than if the light switch was turned to the "off" position. I'm sure that Honda wants to make sure that they have the "CYRE" clause ("RE" stands for "Rear End"). With all of the different possible car owners in the world...there's got to be those people out there who drive their car once a month, but get into it every day to read a book, use it for a pantry, or escape from their annoying room mates.

I was gone for a couple of weeks recently, and left the switch on "Auto" and didn't have any problem at all with it.

And Crashmaster...we all appreciate your knowledge and research. Thanks!!!
 
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