How Long Does It Take to Fully Charge a Car Battery at Idle Speed?

[MaciRose]

It generally takes about 12 hours to fully charge the battery at idle speed. The time required for a full charge during idle depends primarily on the remaining battery level and the battery's storage capacity. If electrical devices in the car are in use during idle charging, it will also affect the charging duration. Most cars use lead-acid batteries. If the battery is nearly depleted and all electrical devices are turned off during idle charging, the process may be more efficient. Whether the car is in motion or at idle speed, the alternator will charge the battery. Regardless of whether it's 15 minutes or just 1 minute, the alternator continues to supply power. The alternator is driven by a belt connected to the engine. Once the engine starts, the electricity generated by the alternator undergoes voltage regulation and rectification before being used to charge the battery. During idle charging, it is advisable to turn off all electrical devices in the car to avoid additional power consumption, which could otherwise harm the battery. At idle speed, the engine's current output is relatively low. If no other electrical devices are used, this low current can help raise the battery temperature, thereby improving charging efficiency.