How long does it take to fully charge a depleted battery at idle speed?

[Sharon]

After the battery is depleted, if the idle speed is 1500 rpm, charging for more than 60 minutes will basically fully charge the battery. The details of charging at idle speed are as follows: 1. It is best to charge while driving, and try to avoid charging at idle speed. 2. Charging at idle speed is possible, but prolonged idling can damage the engine. 3. If the vehicle idles in place for a long time, carbon deposits will form in the engine combustion chamber. 4. The charging effect at idle speed is generally not ideal. Idling the car for ten minutes does not charge as much as driving ten kilometers. This is because the generator produces very little electricity at low speeds, and only during normal driving does the generator's current reach the designed standard current. 5. Idling the car in place can lead to exhaust poisoning. If this happens in a garage, the risk of accidents is significantly higher.

[DelClaire]

Last month, my battery died and left me stranded on the elevated highway. The tow truck driver said while connecting the cables: 'Modern cars have much higher charging capacity than old ones, but idling still charges inefficiently. The AGM battery in new cars with start-stop systems needs over 90 minutes of idling to fully recharge after depletion. The key is to watch the voltmeter - during initial charging, voltage gradually climbs from 12V to 14V, and it needs to stabilize at 14.5V for 20 minutes to ensure safe starting. Frequent battery depletion is a warning sign - it might indicate a faulty voltage regulator, like my BMW that needed 2000+ RMB in parts replacement.'

[McRuby]

Once I forgot to turn off the dashcam during a two-week business trip, and the battery was completely dead when I returned. The mechanic taught me a trick: after jump-starting, don't turn off the engine, set the heater to the highest temperature and maximum fan speed. This forces the alternator to work at full capacity, increasing the charging current to around 50A. Actual tests showed it's 40% faster than idling alone, and 25 minutes of charging provided enough power for a cold start the next day. However, he said car batteries are like elderly people - each deep discharge shortens their lifespan, and it's more reliable to spend 300 yuan on a new one.