Yes — idling your car can charge the battery, but how well it charges depends on whether you have a petrol/diesel car or a hybrid/electric vehicle, and the conditions of the alternator, battery, and electrical load.

What is Idling in a car?

Idling is when your car’s engine is running but the vehicle isn’t moving.
Examples:

Stopped at a traffic light
Waiting in a parked car with the engine on
Warming up the engine while stationary

Does idling your car charge the battery?

1. Petrol/Diesel Cars (ICE Vehicles)

Yes, idling charges the battery, because the engine spins the alternator, which generates electricity and charges the 12-volt battery.

✔ How it works:

When the engine runs, the alternator produces power.
A voltage regulator controls this output.
Extra power is sent to the 12V battery for charging.

✔ Typical charging voltage:

13.7 to 14.7 volts while idling
(this confirms the battery is receiving charge)

✔ How much charging at idle?

Slow and weak compared to driving.
At idle, the alternator spins slowly → lower output.
It may only deliver 10–30 amps, whereas at driving RPM it may deliver 60–150 amps.

⚠ When idling may NOT charge properly:

High electrical loads
- AC blower on high
- Headlights
- Heated seats
- Rear defroster
- Audio system
These may use more power than the alternator produces at idle → the battery could still drain slowly.
Weak alternator
Failing battery
Very low idle speed

✔ Bottom line for petrol/diesel cars:

Idling WILL charge the battery, but slowly and inefficiently.
It’s fine for a small top-up but not for recovering a deeply discharged battery.

2. Hybrid Cars (Toyota Prius, Honda City Hybrid, etc.)

Hybrids DO NOT charge the 12V battery from the engine directly.

Instead:

The petrol engine charges the high-voltage hybrid battery.
The hybrid battery then supplies a DC–DC converter.
The DC–DC converter charges the 12V battery.

✔ Does idling help?

Yes — but only if the engine turns on.

If the car is idling in “READY” mode:

The hybrid system monitors the 12V battery.
If voltage drops, the engine automatically starts and charges the HV battery.
The HV battery then recharges the 12V battery.

✔ Good news:

Hybrid cars are excellent at keeping the 12V battery healthy.

3. Electric Cars (EVs)

EVs do not have an alternator and do not idle (the motor doesn’t run when stopped).

But they can still charge the 12V battery while stationary.

✔ How EVs charge the 12V battery:

A DC–DC converter pulls power from the main traction battery (e.g., 400–800V)
and steps it down to 12–14V to charge the small battery.

✔ So does “idling” in an EV charge the battery?

Yes — but:

You must have the car in “ON/READY” mode.
The main battery slowly discharges to maintain the 12V battery.
No need to run a motor.

How Long Should You Idle to Charge a Weak Battery?

For petrol/diesel cars:

20–30 minutes of idling can add a small boost to a moderately weak battery.
To fully recharge a deeply discharged battery, you’d need hours — impractical.

For hybrids:

Just leave it in READY mode; the system will take care of charging automatically.

For electric cars:

The 12V will be charged automatically as long as the car is awake.

Important Limitations

Idling cannot:

Fully recharge a dead battery
Fix a failing battery
Charge fast enough in very cold conditions
Keep up with heavy electrical drain

Idling can:

Add partial charge
Maintain a healthy battery
Help a slightly weak battery recover
Provide enough boost to start the engine

Final Summary

Vehicle Type	Does Idling Charge the Battery?	How?
Petrol/Diesel (ICE)	✔ Yes	Alternator charges battery at low output
Hybrid	✔ Yes	Engine → HV battery → DC–DC → 12V battery
Electric (EV)	✔ Yes	Main battery → DC–DC → 12V battery
Best charging method	❌ Not idling	✔ Driving or ✔ external charger