Does a car need to be started to charge after replacing the battery?
3 Answers
It depends on the situation. If the battery has a charge indicator, you can check the indicator to see if the battery is fully charged and does not need charging. If there is no indicator, you can also use a voltmeter to measure the open-circuit voltage of the battery. If the voltage is above 12.75V, no additional charging is required. Newly purchased batteries are generally not fully charged, but they are not too low either, so there is no need to worry too much about power loss. As long as the engine is started, the battery will automatically charge. As for how long it takes to charge a car battery, generally speaking, driving normally for one to two hours is sufficient to restore the battery to normal charging levels.
Should I start the car to charge a newly replaced battery? Let me tell you, actually new batteries come fully charged from the factory. However, based on my observations over the years, I've found that many 4S stores and repair shops keep batteries in inventory for several months, during which the charge gradually decreases. So every time I replace a battery, I always start the car and let it idle for ten or twenty minutes. This allows the alternator to replenish some energy to the battery, and by the way, I can check if the dashboard voltage stabilizes around 14V. Most importantly, this enables the vehicle's computer to re-recognize the battery parameters, especially for cars with start-stop functionality. If you simply turn off the engine, lock the car and leave, the next startup might feel weak and sluggish. Although my neighbor drove off without charging last time and had no issues, for safety's sake, it's better to charge it for a while.
As a tech-savvy person who often helps friends with car repairs, I recommend engine charging. A new battery's resting voltage should be around 12.6V, but it may drop below 12V after prolonged storage. Once the car is started, the alternator takes over the charging task—don't rush to turn off the engine at this point. Let it idle for 15 minutes or drive a few kilometers to fully recharge the battery. This approach has three benefits: it prevents deep discharge from damaging the battery's lifespan, allows the ECU to relearn the battery parameters, and most importantly, checks whether the charging system is functioning properly—what if the alternator has an issue? Don't worry about the small amount of fuel consumed; batteries are far more expensive than gasoline.
