You might be surprised to learn that many modern cars can suffer a dead battery with as little as 2 – 4 weeks of not being driven. Many higher end cars only need as little as two weeks before the battery can die due to non use.
This isn’t to say that it’s a hard and fast rule. It just means that with modern cars using the battery for various applications even when the car is not being driven, the battery is being used at all times and it adds up. The question becomes how to maintain your car battery during a vacation, lockdown or other times when it’s not being used.
The ideal way to charge your car battery is to drive your vehicle for at least 20 minutes every 3 weeks and to avoid only driving short distances. Idling your engine is illegal in a growing number of jurisdictions and may do the battery more harm than good. Using a trickle charger will keep the battery charged when the car isn’t in use.
Is it illegal to let your engine idle?
Before we talk about the value of idling your car engine to recharge your battery, is it even allowed in your home area? Some jurisdictions outlaw idling a car engine for more than several minutes due to the pollution and emissions produced.
23 states plus Washington, DC limit engine idling by some or all vehicles. In Colorado, Connecticut, Delaware, Maryland, Massachusetts, New Hampshire, New Jersey, Texas and Vermont it’s illegal to idle your engine for more than 3 – 5 minutes.
Many other states limit the idling time of certain vehicles such as school buses and government-run vehicles. According to the US Department of Energy, eliminating engine idling is equivalent to removing 5 million vehicles from the road
so it’s a growing concern related to air quality and pollution.
So even if idling your engine is an effective method of recharging your battery, it might not be allowed in your home area. But if it is allowed, the question is how long would you have to idle your car engine in order for it to make a difference to your battery?
How long should I idle my car to charge the battery? Does it even work?
There is conflicting information online regarding whether or not idling a car helps to recharge the battery. While some people suggest that idling a car for up to 10 minutes will recharge it, others suggest that simply idling a car doesn’t do enough to make a difference and may actually do more harm than good.
I came across an article from an electrical engineer who tested the theory and worked out that it could take up to 4 hours of idling an car engine to fully charge a battery. Clearly, that isn’t doable or efficient regardless of what the local laws are on idling.
One school of thought says idling a car does allow the car battery the chance to recharge. The other says that a car needs to be driven for a period of time above idle speed to properly recharge it.
Who is correct and what are the specifics you should follow to keep your car battery healthy and charged? I decided to contact the major car battery brands themselves and here’s what I found.
Recharging your car battery by idling: What the car battery manufacturers say
I decided to contact some of the major car battery brand manufacturers and resellers to see what they say in terms of idling and recharging them. I asked them specifically about whether or not idling a car would properly recharge the battery. Here’s what their respective customer service department said in response.
Interstate Batteries: Yes, that will recharge your battery.
BatterySystems.net: While idling your vehicle may give it enough of a charge to restart, this approach is generally not recommended. You are much better off driving the car for 20 to 30 minutes every three weeks.
Optima Batteries: Generally, running the engine at idle or short stop-and-go trips, during bad weather at night, will not recharge the battery effectively. With any battery, a voltage below 12.4v has the potential to produce sulfation. This will reduce the performance of a battery by prohibiting the chemical reaction that causes the battery to hold its charge. This can be reversed as many chargers have a “de-sulfating” mode which pulses a charge into the battery. Even charging an Optima at a 10 amp charge can help reduce this. Cycling the battery a few times can also help if the battery is severely sulfated.
Optima Batteries’ response was far and away the most detailed one I received. They also went on to mention that your ability to recharge your battery using your alternator (ie. while driving) is based on:
1) How much current (amps) from the alternator is diverted to the battery to charge
2) How long the current is available (drive time)
3) Battery temperature
4) Battery age
So when you think about it in detail, charging your car battery by actually driving your car isn’t even just a matter of driving it for X minutes but other factors that come into play too.
Recharging your car battery by idling: What other professionals say
Battery manufacturers and distributors aren’t the only ones chiming in. Here’s a specific response from the Canadian Automobile Association (CAA) in terms of why idling a late model car to recharge the battery isn’t a good idea and may not even work:
Many modern cars are equipped with sophisticated battery management systems that are designed to help extend battery life. As such, this technology may also limit your car’s ability to charge at low RPMs. Unless you’re moving at higher speeds, the battery may be getting little charge.
CAA
And here are some thoughts from auto parts distributor NAPA:
Relying on an alternator to keep a dying battery going is a bad idea in any case, as it was never intended to play that role and can lead to eventual burn-out. If your battery is dying, replace it, and if it needs to be charged, use an actual battery charger and not your car’s alternator.
NAPA
Maintain your car battery during a lockdown and when not being driven
Other than driving your car regularly, how can you maintain your car battery to ensure it remains healthy and charged?
Here are several options to consider:
Use a trickle charger
A trickle charger is an electronic device you can use at home to keep your car battery maintained. A trickle charger charges a car battery and is especially useful for older cars, cars with older batteries and whenever you won’t be using your car for an extended period such as a long vacation, winter or a lockdown. You attach the charger directly to the car battery and plug it in to a socket.
Depending on the model, a trickle charger can charge the battery at different rates and may or may not shut off automatically when the battery has been fully charged.
Higher end models have faster charge times and more options such as battery maintenance functionality and the ability to charge batteries for not only cars but SUVs, boats, ATVs, classic cars and more with varying levels of voltage.
Trickle chargers cost $30 for entry level models and go up to $100 for more powerful featured options.
Use a regular car battery charger
A car battery charger is different from a trickle charger. While a trickle charger is used to recharge a battery and keep it at a highly charged level, a regular battery charger can be used to bring a dead battery back to life. So if your car is stuck in the garage with a flat battery like I once experienced, you can connect it to the battery charger and jump start your car. Except this jump start doesn’t require another person’s car helping you out.
Higher end models also provide battery and alternator testing features to show you charge level and diagnose electrical problems. They also include auto voltage detection features so you don’t have to know in advance whether you have a 6V or 12V battery.
Car battery chargers typically cost $60 – $120 although you can spend even more on larger more powerful units capable of jump starting large diesel engines.
Ask your mechanic to recharge your battery
Can your mechanic recharge your car battery? Yes they can but it’ll most likely be for a fee. Your local garage can test your car battery for its level and overall health and can also top it up so to speak so that it’s charged.
Some mechanics offer a free battery test and charge especially if you’re paying for other work so ask when making an appointment if they offer these services. Otherwise expect to pay $10 – $20 for a battery recharge. The older your battery the more it can benefit from a recharge but at some point every car battery loses its ability to hold a charge and will need to be replaced.
An unused car hurts more than just the battery
While the battery is the obvious part of your car to suffer when the vehicle isn’t driven for an extended period of time, there are other considerations for your unused car:
- Battery-related issues with other parts of your car such as malfunctioning lights and sensors, door lock problems or warning lights popping up randomly.
- Flat spots on your tires when they are not rotated regularly. Flat spots can appear after 3 months of a vehicle not being driven but will typically even out with driving. Permanent flat spots may occur from 6 months or more of a vehicle being parked in the same spot.
- Rust and corrosion collecting on the brakes and rotors.
- Lack of circulation of oil and other fluids can lead to moisture build up.
How to extend the life of your car battery
- Drive your car regularly and try to avoid only taking short trips of several minutes in length that involves stopping and starting the engine.
- Clean the battery cables and keep them clean. Don’t allow them to get corroded.
- Get your battery checked and tested each time you go for a car servicing.
- Buy a battery tester and test the battery yourself to monitor its charge over time.
- Use a trickle charger to keep the battery charged at home.
- Ask your mechanic to recharge your battery in spring after the winter or just before winter begins since that’s the season that tends to use the most power for heating and defrosting.
Summary
Idling your car to recharge the battery is not an efficient way to accomplish this and increasingly isn’t even allowed in many jurisdictions that limit idling time to 5 minutes or less if at all. The alternator in your car was not specifically designed for the purpose of helping you use a battery that should be replaced. A battery charger or trickle charger is a better option to extend the life of a car battery. And at some point, you just need to bite the bullet and buy a new battery.
The more you regularly drive your car, the better the health of the battery and the car in general since it is meant to be driven. The older your battery gets the more likely leaving your car sitting for weeks or longer will negatively impact the battery life and increase the chance it dies without warning.
If you’d like to learn more about car batteries including my experience with changing them and dealing with a flat battery in the garage, check out my article called Stuck In The Garage: Why Don’t Cars Have Battery Meters?