Do car batteries charge while idling?

The car battery is one of the parts that need to be changed at a certain amount of time because it will wear out. However, drivers that use the car rarely or drive more short distances than long distances are more prone to change the car battery more often, because of problems with battery discharge.

The short answer is yes, car batteries do charge when the car is idling, because of the alternator that becomes the main power source of the battery and the entire electrical system of the car. If you have a working alternator then the battery will receive current all the time when the engine is on.

When the car is idling, there is no load on the engine, but some processes will run during this time, such as maintaining the working temperatures for the oil and coolant and maintaining the engine’s working state overall.

How alternator helps the car battery to charge while idling?

The opinions of those in the automotive field are divided regarding the fact that the alternator begins to give sufficient charge to the battery already at idle speed. The fact that the alternator charges the car battery only when the car is moving is completely false. Receiving power from the alternator does not depend on the movement of the wheels.

What if you are in constant traffic jams and the car is idling more than in motion? That will mean the engine will stop, and that does not happen unless there are problems.

In an internal combustion engine, generating energy is based on some principles. To start the car, an electric motor, also called a starter, is switched on by the car battery, providing the initial crankshaft rotation which transmits torque to the wheels.

The battery gives a large current when the engine starts, this is called the starting current, and its value can reach 300 – 400 Amperes.

In many cars, various belt drives are hung on the free tail section of the crankshaft. Thus, a small part of the torque is used to rotate the shaft of the automobile’s alternator. The engine crankshaft and the alternator’s rotor rotate synchronously.

The car’s alternator has a rotor (rotating part) with a winding and a stator (stationary part) with a winding. It also transforms alternating current (AC) into direct current (DC) and the resulting current will be transferred to the car battery to charge it.

So for this process wheel movement is not necessary, the rotation of the crankshaft is enough to generate current for the car’s battery and other parts that need it, so it will work even when the car is idling.

Do alternators generate enough energy for the battery?

Alternators are designed to produce as much energy as the batteries and other consumables need to function properly. If for some reason, there is a problem with charging, the driver will be informed, most of the time, by a light indicator that appears on the car’s dashboard in the form of a red rectangular icon with “+” and “-” signs.

The car’s total power consumption is enough for the alternator to withstand without the help of a battery. When certain values ​​are reached, the system will draw energy from the battery to reduce the overload.

When the engine starts, this dashboard indicator will light up for a few seconds. If the indicator does not disappear, this indicates a potential problem with the DC supply, most of the time the reason will be a failing alternator. A diagnostic, however, must be performed to restore the electrical system to working order.

Charging the battery when idling in winter

Charging the battery does not depend on the season. At cold temperatures, it should be noted that battery charging is slightly slower, however, it will improve when the engine warms.

The main reason why the battery will drain faster in the cold season is frequent short trips because no sufficient current is obtained, which gradually leads to a complete battery discharge, so you should be careful in winter with the short trips. Just drive 10-15 minutes longer, it will be enough.

It will be difficult to recharge if the majority of consumers start drawing energy for themselves. There will also be difficulties in winter because the battery takes less current in the cold.


The alternator’s job is to supply the battery and the other consumers in the car such as headlights, fog lights, alarms, central locks, radio, a better sound installation, etc. that puts some pressure on the electric system.

This process of charging does not have conditions, the alternator can charge the battery whether the engine is idling or the car’s moving, as long as the alternator and the battery are in good working conditions there won’t be any problems with charging.

The battery takes exactly as much charge as it has spent (say for starting) and no more. If you always charge the battery, then it will simply boil and can blow up.

The charging won’t be affected unless there is a problem with the alternator, the battery is worn out and on the car is installed a consumer who turns the whole process of power supply upside down.

When the engine is idling and the battery is not charging properly, this can be due to a consumer that it’s problematic, most often incorrectly installed in the car. So you better check those consumers.

Also, other car enthusiasts will want to install in their cars other electrical consumers which will need a bigger battery and also a better alternator to cope with the new load.

Manufacturers set their idle values ​​for different car brands. If some indicators, in reality, turn out to be lower, then this is a sign of imbalance in systems and processes.

If the car stands for a longer time, that does not mean that the battery will not waste its energy, on the contrary, it will drain much faster than a car that is frequently driven, and, of course, there are enough consumers who can bring the power source to zero performance in no time.

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