Can the car battery be recharged while the engine is idling?

Whether it is because we have more than one vehicle at home and one of them is rarely used, due to the confinement situations we live in with the coronavirus pandemic, or because your car has run out of battery and you have started it with the help of another car using a clamp, many users wonder whether it is good to start the car and keep it idling so that the battery does not discharge… or to recover the lost charge. The answer is yes, but with nuances. As we already mentioned in this article with tips for maintaining your car during the pandemicthe ideal way to preserve the battery if the car is going to be stationary for a long time is to start it up at least every 10 days, approximately. But we also insisted that the best thing to do is to move the car and drive it, even if it is only a short distance. And not only for the battery, but also for other elements: the engine itself, the tires, the air conditioning system, etc. However, there are many users who still ask us about the advantages or possible disadvantages of occasionally starting a car that does not move much and leaving it idling for a few minutes, so that the battery does not discharge completely. The first thing to bear in mind is that not all cars have an alternator. alternatorworks in the same way. And that this measure to start the car and to put it to the idle will also depend on the own state of the battery.

Charging the battery while the engine is idling

Note that when the car is idling, the alternator, which generates the electricity needed to power the car’s electrical components, will have very little capacity to recharge the battery. The alternator’s capacity to generate electrical power depends on the engine speed. In fact, it may happen that if you leave the engine idling for a very short time, there is not even time for the battery to recover the amount of energy it needed to supply for starting.

At this point, you are probably asking yourself two questions: Is it better to accelerate the car at idle speed so that the alternator spins faster and the battery recharges sooner? How long do I have to let the car idle?

The answer to the first question is yes: when you accelerate you increase the current supplied by the alternator. But it is not good for the engine to idle until it is at optimum operating temperature. And much less to make it turn high revs. As for the second thing… it depends on the battery, the car… Bear in mind that starting the engine and keeping it idling, most cars do not manage to restore the battery to its optimum state of charge (between 90 and 100%). If they did, it would take hours…

The problems of leaving the car idling

When the vehicle is stopped for a very long period of time, resorting to starting the car and leaving it idling can be harmful, so caution must be exercised. It is important to know that cold starts are when the most wear occurs, until the oil in the lubrication system reaches all parts of the engine. Another negative element is that during combustion, water is produced which can have a double harmful effect if the car is not running.

On the one hand, the oil can become contaminated more quickly. For this reason, a car that does few kilometers per year but with many cold starts (typical very short trips several times a day) needs shorter oil change intervals than a car that drives more kilometers, but with few cold starts and a lot of highway driving.

In addition, without reaching temperature, the water vapor does not evaporate and can cause internal corrosion in the exhaust system. Not to mention the particulate filter in diesel enginesThe particulate filter in diesel engines would fill up with ash that could not be removed because the temperature required for its regeneration was not reached.

It is clear then that starting the car and leaving it idling to preserve the battery can be a worse solution than leaving it stopped for several weeks, and looking for a way to go out to drive, or directly using a battery charger. It can be a measure to use if you do not have another solution, always bearing in mind the mentioned considerations: to let the car to take temperature, not to accelerate it too much in idle, and not to leave it too much time in march, at the most between 10 or 15 minutes.

Related information of interest

• Be careful with the battery! In winter, the condition of the battery must be monitored more closely
• How to jump start a car with the clamps if the battery is dead