Automotive

Will battery get charged when car is sitting idle, or you have to get it onto highway?

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  • Nov 16th, 2018 10:07 pm
Member
Nov 27, 2009
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Will battery get charged when car is sitting idle, or you have to get it onto highway?

Battery died and had to jump start the car. Now have a question about charging the battery.

Normally I will drive my car on the highway for a while to charge the battery, but it is snowing outside and I am thinking if it is possible to charge the battery other than running on the highway? So

1. If you park your car in your garage and jump start it, then let the engine run for a while (say, half an hour or longer). Will it charge the battery? Or you have to get the car onto the highway?

2. If the alternator does charge the battery when the car is sitting idle, is it better to sit in the car and step on the gas pedal so that it charges faster?

3. Is there any other method if you do not want to bring your car onto the highway to charge the empty battery?

Thanks.
24 replies
Deal Addict
Aug 10, 2013
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Get a battery tender with a pigtail (noco genius g3500). Easy to unplug when you dont need it

Idle isn't doing any charge for your battery
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Feb 11, 2007
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Ideally you should charge it with an intelligent battery charger. Also keep in mind that draining your battery dead will take life out of it.
If you don't have a charger, you can charge it while parked, but if you want a proper charge you'll want to rev it above idle. To be sure, you could measure the voltage at idle and above to find where it charges best.
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Deal Fanatic
Nov 1, 2006
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Charging while idling will charge your battery but slowly. If your car is a few years old, alternator brushes are a little worn so output won't be as much as when new. Also, factor in the electrical load from daylight running lights and other electrical loads, This is why a highway run is usually recommended if a charger is not available. IME, the best way to recharge a battery is to remove it from the vehicle and charge it indoors overnight or even longer.
Last edited by Jimbobs on Nov 14th, 2018 12:56 pm, edited 1 time in total.
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The more important question is: why did your battery die?
Deal Expert
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Your car may not charge your battery as much as you think it would, especially if you have a newer car. Many newer cars (ie less than 7 years old or so) have smart/eco-charging systems where the alternator may not run all of the time your engine is on in an effort to save gas. As a result, when you think that the car is charging your battery, it really isn't. Even if you don't have an eco/smart charging system in your car, just driving your car for a few miles on the highway won't do much to charge your battery especially with Winter being here. Cold car batteries charge slower than warm car batteries. And even if you were able to drive the car long enough (ie for an hour or more at highway speeds), you won't have a full battery... at best, it would be 70 to 80% full.

Given the price of gas these days, a decent low-end charger is very reasonable these days at about $30 to $40.
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^ this. If your battery is dying it's a sign you need to get it checked out/replaced, or there is an issue with your vehicle's charging system or system/accessory power draw. Most likely you need a new battery, but it could be any one of those things, or some, or all combined. Age, short trips, and infrequent use will be very hard on the battery.
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A few things you didn't mention were Make, model, age/mileage of your car and your driving pattern.

I've had batteries last 14 years and other only 5 years. The ones that lasted the longest were in cars that were used for 40km commute each way and left sitting otherwise. The ones with the shorter lives were used in cars that did lots of short trip every day.

I know this isn't the only determinant of battery life but it's definitely a factor.
Deal Guru
Sep 1, 2004
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derass wrote: The more important question is: why did your battery die?
If you drive it daily, this question should be answered 1st.

1) you may have a bad alternator

2) you may have a bad battery

3) If you park outside in sub 0 temp and battery isn't charged, battery is probably frozen and totally dead.

4) If you park inside in room temp, then you may have to look into parasitic draw. Looks for corrosion at the leads and clean those up. In this case, if battery still good, a charger could be an answer.
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Jimbobs wrote: A few things you didn't mention were Make, model, age/mileage of your car and your driving pattern.

I've had batteries last 14 years and other only 5 years. The ones that lasted the longest were in cars that were used for 40km commute each way and left sitting otherwise. The ones with the shorter lives were used in cars that did lots of short trip every day.

I know this isn't the only determinant of battery life but it's definitely a factor.
To a certain extent, usage and charging patterns are a large determining factor. By in large, the actual starting of the engine is the hardest thing the battery has to do in its life as it requires lots of current to move the starter and provide the spark (hence the thick wire to the starter). The more starts, the more it takes out of the battery. If you look at cars equipped with engine start/stop, many of them are equipped with special start/stop batteries and the ones that aren't suffer from battery issues. Long drives allows the battery to recharge to a sufficient stated to keep a lot of the sulfation at bay where shorter drives won't recharge the battery enough to do. By investing in an external battery charger, you are basically simulating a long drive but better as a long drive won't get your battery over 80% while a charger will get that same battery to over 95%. As a bonus, you save gas and time.
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M1K3Z0R wrote: ^ this. If your battery is dying it's a sign you need to get it checked out/replaced, or there is an issue with your vehicle's charging system or system/accessory power draw. Most likely you need a new battery, but it could be any one of those things, or some, or all combined. Age, short trips, and infrequent use will be very hard on the battery.
It's not necessarily a sign that it needs to be replaced but it does need attention - ie topping off of fluids if possible, charging and then testing. Many good batteries have been replaced without much thought when all that was needed was some care and attention.
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Xtrema wrote:
3) If you park outside in sub 0 temp and battery isn't charged, battery is probably frozen and totally dead.
Dead may be the wrong word for it. Most people associate a dead battery with one that is out of charge or the state of charge is below an usable amount.

A frozen battery will typically suffer from physical damage to the plates (may deform or crack them) as the battery acid expands (due to it being frozen). This damage may cause a cell to short out or become disconnected causing the battery not to function. Depending on the state of charge of the battery, batteries can go down to -60C before freezing if fully charged while a dead battery (one that has a very low state of charge) may freeze just below -5C.
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A working alternator will charge the battery when idling.

It may charge faster if you rev the engine, or it may not. My ex had an 81 VW that would only read about 13v at idle but over 14 if it was rev'd up. My current cars are capable of full power at idle.

The modern eco-modes on cars doesn't affect this point, they generally will charge for a few minutes after startup, and they'll only enter eco-mode if the battery is fully charged.
Member
Nov 27, 2009
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Thank you for all the replies above.

My car has been parked outside for couple of weeks, so the battery couldn't start the engine due to recent temp drop and/or possible bad quality.

I find the Costco Kirkland battery pretty bad. This is my 2nd Kirkland and was bought in mid 2016 (could be 3rd, but none of them lasted more than 3 yrs).
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Nov 27, 2009
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One more issue: now the battery is so low that I couldn't even open the door (and so couldn't open the hood to do jump start).

Do I need to call CAA to open the door or is there any quick method? (I do have CAA membership but trying to see if I can solve the problem myself.)
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Jun 14, 2008
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A couple of weeks parked can definitely drain the battery.

Get a battery charger/maintainer to charge it and keep plugged in when you park it for extended period of time. I think I saw battery tender jr. at home depot for less than $30.
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cddc wrote: One more issue: now the battery is so low that I couldn't even open the door (and so couldn't open the hood to do jump start).

Do I need to call CAA to open the door or is there any quick method? (I do have CAA membership but trying to see if I can solve the problem myself.)
Is there not a keyhole in the door handle? If there is this may be the stupidest post of the year!
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What if there's no visible key hole outside the stupid car/vehicle?

Edit: Found it.

Last edited by Bb0231 on Nov 14th, 2018 4:20 pm, edited 1 time in total.
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Then it might be under a small cover, and the keyfob might contain a key if you open it up.
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Bb0231 wrote: What if there's no visible key hole outside the stupid car/vehicle?
Check the trunk
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