Idling: it's far from ideal.
Lastly, you may have heard that idling your car for 15-20 minutes is a good alternative method to recharge your battery. While idling older vehicles for 15-20 minutes may give them enough of a charge to restart, this approach is generally not recommended.
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.
The engine contaminates the car’s oil faster reducing its ability to protect the engine. Cars are not designed to idle for an extended time so the increased exhaust particles will begin to carbon-up the engine causing lack of performance, increased emissions and eventually component failure (i.e. catalytic convertor).
Condensation builds up in the exhaust and without the high airflow from driving, the vehicle isn’t able to blow this buildup of water out of the tailpipe. Eventually, this will cause the exhaust system to rot and prematurely fail.
The exhaust generated from your vehicle pollutes the air even more so than normal. More exhaust particles are created through idling than at any other time which is bad for the environment and for our combined efforts to reduce our carbon footprint.