How long should you let a car battery charge

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When Does a Car Battery Charge?

We ask a lot of our car batteries, don’t we?  I mean we depend on them to get our car started and sometimes we depend on them to charge our ever-important devices.  Now, we have discussed at length what to do when a car battery dies.  But with all the stuff a battery does, have you ever wondered when the car battery has time charge?

Really the battery is charging every time the car is running.  The alternator keeps a constant flow of AC power running to the battery.  The alternator is producing power every time the car is running.  Ergo the battery is being charged the entire time the car engine is running.  

I highly encourage you to watch the following, very entertaining video, that explains it in great detail:

It should be noted that this is assuming the car battery is in good health.  There will come a point in a battery’s life when it will no longer hold a charge. Now some of you may be wondering do car batteries charge while the car is idling? Let’s Discuss.

Do Car Batteries Charge While the Engine Is Idling?

The answer is ‘YES’, yes the car battery does charge while the engine is idling.  Again, assuming that the battery can still hold a charge.  Again, I encourage you to watch the video above, this answer will make more sense.

As long as the mechanical action of the alternator is taking place; that is, being turned by the engine crankshaft.  Then the alternator is producing AC current, thereby charging the battery while your car is idling.

How Long Should I Idle my Car to Charge the Battery?

So this is an interesting question, that came up during my research.  During these times of the Coronavirus many of us have our vehicles sitting much longer than they ever had.  Even if your area is ‘opening up’ you are likely not driving as much as you once did.  So is it a good idea or even worth the energy spent to let your engine idle to recharge your battery.  

In this article from Jalopnik, they interview an electrical engineer who tested a 2019 Toyota Tacoma.  If you want a lot of technical jargon the article is worth a read.  But the summary is this.

You would have to allow your car to idle for possibly several hours to completely charge your battery.  There are many electrical systems in your car all vying for a little bit of power from the alternator.  What energy is left over to recharge the battery is very small.  

There are a number of variables to this.  The amount of computer and electrical systems in your car, the health of your battery, and how much voltage your alternator is producing.

So allowing your engine to idle may put a small amount of charge on your battery, but that may not be the most efficient way to charge your battery.  The conclusion of his study estimated that allowing your car to run for only fifteen minutes or so would actually cost you more energy than you would gain.  

So, is it a good idea to allow your engine to charge your battery, it would not seem so.  Go for a drive instead, you need to get out of the house anyway, right?

If you feel like your car will be parked for a while, putting a trickle charge on your battery (click here to see my recommended trickle charger) would probably be the best solution.  This will keep a low amount of voltage applied to your battery to keep it from going dead.

How Does A Car Charge a Battery?

I will refer you back to the video above.  It will explain better than I can about.

However, if you aren’t interested in the video I will try to give you the Clif’s Notes version of how a car charges a battery.  

It starts with the alternator, the powerhouse of your car.  The alternator is connected to the crankshaft of the engine via a belt.  As the belt turns, it spins a rotor, surrounded by magnets, inside the alternator.

As the rotor passes the magnets it creates an AC current; which is converted to a DC current and then distributed throughout the vehicle.  Providing electricity to all of the electrical components in the car and then finally charging the battery.

Simple, right?

How long does it take a car battery to charge while driving?

So you have decided to go start your car and take a little drive to get a change of scenery. Or you have jump-started your car after it has sat too long.  You may be wondering how long it will take your car battery to charge while you drive around?  The general consensus is you have to drive the car at least 30 minutes to put any meaningful charge on it. 

This is not to say that driving for 30 minutes will fully re-charge your battery.  There are several factors to consider.  1) How much was your car battery depleted?  And 2) The overall age and condition of your car battery.  

If your car battery has been sitting for some time, then driving it around for 30 minutes may not fully recharge it.  But not all is lost, driving it around will put some charge on it and keep the car battery from going completely dead.

Sometimes the condition of the battery just doesn’t allow it to hold a charge anymore.  I will once again cite my trip to New Jersey from Florida.  I had hours and hours of interstate travel, it didn’t matter, my car battery was not holding a charge anymore.  It was time for it to be replaced.

Final Thoughts…

The car’s electrical system is a complicated thing.  Hopefully, you know understand now when a car battery is charged and how.  The battery is just one component in a complex circuit.  The car alternator is the real power plant in the vehicle, now if that goes bad, it’s a whole different story that we will discuss later.

Keep an eye on your battery, drive it around a bit, know how old it is.  Stay safe and 

Safe Travels.

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