Recharging car battery

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Well, I did it again. Got in car, key turns in lock, uh-oh FFFFFF Left my lights on AGAIN!
Knocked on several neighbor doors; nobody home to give me a jump w/my cables. Had to call road service.
Question: WHY does engine have to run only 20 minutes; doesn't even have to be driven to recharge battery enough to drive and be able to shut off and start again? This has been bothering me for years.
HB
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The length of start is only seconds. 10 amps times 20 minutes equals 1200 amp seconds into battery. 1200 divided by 3 seconds equals 400 amps for 3 seconds out out of battery. Might be right or wrong, it's late.
Alternator must be higher in rpms to deliver anywhere near max output, so driving is better than idling.
Greg
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On Mon, 30 Jun 2014 07:24:26 +0000 (UTC), gregz wrote:

A typical BMW Bosch alternator is 120 amps (160 for the higher performance bimmers). That's a LOT of current.
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On 06/30/2014 03:00 AM, Higgs Boson wrote:

http://smile.amazon.com/Schumacher-SE-1052-Manual-Starter-Charger/dp/B000AM8BF4
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On Mon, 30 Jun 2014 00:00:03 -0700 (PDT), Higgs Boson

The alternator has a much higher output than the typical battery charger so it does not take very long to get it up to snuff again. But discharging like that is not good for overall battery life.
Do you have a very old car? I think it was in the 70's that most cars had a buzzer to let you know the lights were left on. For quite a few years now, automatic lights have been available.
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On 6/30/2014 6:08 AM, Ed Pawlowski wrote:

doesn't even have to be driven to recharge battery enough to drive and be able to shut off and start again? This has been bothering me for years.

Good answer. Most car alternators have good output, even at idle. I've read and heard that deep discharges are damaging to car or other lead acid batteries. So, leaving lights on over night will shorten the lift of the battery, and may kill it totally.
Perhaps HB might be wise to buy a car battery charger, and have a neighbor show her how to use it? You could run extension cord from the house, and put the charger on. Faster than the response time of the tow service.
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On 6/30/2014 7:42 AM, Stormin Mormon wrote:

Some chargers have a "jump start" option too.
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On Monday, June 30, 2014 4:42:09 AM UTC-7, Stormin Mormon wrote:


Yikes!!! What should I do, Stormie? and you other guys. It's a relatively new battery - 2-3 years --so I don't want to kill it!! Should I do more long-distance freeway driving rather than just dick around town??? Or what?

I actually asked the road service guy about that. He said some were very expensive (I think I could make out $400???) but some less so.
Basically I should just be MUCH more careful!!! Let this be a lesson to me.
Thanks to all.
HB

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On Monday, June 30, 2014 1:53:52 PM UTC-4, Higgs Boson wrote:

Just don't leave the lights on. Doesn't the car have a chime that alerts you if you go to exit the car with the lights left on? And despite what some are claiming here, I've run lots of batteries down over the years, many times, and it didn't kill them. If you use a car battery as a deep cycle battery and do it every day, yeah the battery isn't going to last long. But if you forget you lights a couple times a year, it's not going to kill a 2 year old battery.

You can get a typical charger for $50 - $75 that will charge it up enough to start in about an hour. You can get one for less if you're willing to wait over night for it to charge. Lower current ones will cost less.
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Long ago I made a simple rule for turning the car off, and enforced it with my children.
When you turn the key off with your right hand, put your left hand on the lightswitch.
If you forget, do not then turn the lights off. Instead, restart the car, then turn it off correctly.
That makes it a habit. Nobody in my family has ever run the battery down by leaving the lights on.
Of course a battery eventually fails and needs a jump. But we've avoided the avoidable ones.
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On Monday, June 30, 2014 12:30:43 PM UTC-7, TimR wrote:


THAT'S A WONDERFUL REMINDER! Hereby adopted.
Now can you give me one to remember to take my cold bag into Trader Joe? I've tried everything, including a Post-it on the wheel which I ignored.
It's not the dime a bag they're charging here now -- it's the mufa PRINCIPLE of the thing. Neurons in what's left of my brain have to make new connections....!!!!
Thanks again for the Mnemonic. (I always wanted a chance to use that unpronounceable word.)
Wikipedia: A mnemonic, or mnemonic device, is any learning technique that aids information retention.
HB
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I might have a problem driving another car right now. Although I have a 66 datsun, I have yet to drive at night with that. My Subaru automatically shuts off the lights. My avalanche just has a mind if it's own. I let it think.
Greg
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On 6/30/2014 1:53 PM, Higgs Boson wrote:

It's a relatively new battery - 2-3 years --so I don't want to kill it!! Should I do more long-distance freeway driving rather than just dick around town??? Or what?
CY: As to the battery, it's a "well, it's done now" moment. Eventually, you'll have the moment when it won't restart, even after running a while. Then, it's time to change. I've tried (yes, and failed) to develop the habit of turn back and look at the lights every time I exit a vehicle. I tried. I've heard short trips can be rough on vehicle if the motor doesn't get a chance to warm up. More to do with oil than battery.

some were very expensive (I think I could make out $400???) but some less so.
CY: Your local department store or auto parts store should have one about $50.

CY: Careful is good.
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On Monday, June 30, 2014 3:08:46 AM UTC-7, Ed Pawlowski wrote:

Well, SOME would say it's "very old" <g>, but it's actually a '99 Nissan Maxima GLE. AFAIK it does not shut off headlights automatically; wish they still made the buzzer. Or is there some setting I have missed?
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On 6/30/14, 2:00 AM, Higgs Boson wrote:

It might be worthwhile to have a mechanic install a relay to automatically turn off the lights when the ignition is off. My Subie has it and it's a nice feature.
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On 06/30/2014 06:44 AM, Dean Hoffman > wrote:

As mentioned, the car's alternator has considerably more output that your typical "home" charger. In 20 minutes it would not fully charge the battery...more than likely 80%. Of course that would be good enough to start the car quite a few times.
A lot of cars have the "turn off feature"
BTW: A 10 or 20 amp battery charger would be a good thing to have. It would cost less than a service call and would probably only take a short time to charge the battery enough to start the car.
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Well, the root problem is that you are a moron. That is shown by
1) You repeatedly do the same stupid thing.
2) You post through GGs.
Get a clue dude.
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philo wrote:

I have a battery tender for the bike , it takes about 24 hours to recharge the truck if I forget and leave lights on . I also have the old <damaged filter cap , tender/sensor circuit blown> charger/power supply from the camper . It puts out 55 amps , and will charge the battery enough to start the truck in under 30 minutes .
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On 06/30/2014 07:53 AM, Terry Coombs wrote:

Since I worked in the battery industry I managed to accumulate a lot of surplus gear. I have one charger that puts out about 120 amps and can start a car with a dead battery. Of course it's very heavy and though on wheels, has only been used in emergencies.
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Stormin Mormon wrote:

If you forget to turn the lights off, would you remember to plug in the charger? Maybe the world needs a wireless charger so you would just have to remember to park the car in the same place.
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