Can You Start the Engine While Charging a Car Battery?

[DiCharlie]

You can start the engine while charging a car battery. Precautions for battery charging include: 1. In cold weather, check if the electrolyte is frozen before charging; do not charge a frozen battery. 2. Before charging, check the electrolyte level; do not charge if the electrolyte is insufficient. 3. During charging, measure the density and voltage of the electrolyte approximately every hour and monitor its temperature. The functions of the battery are: 1. To supply power to the starting system, ignition system, electronic fuel injection system, and car's electrical systems when starting the engine. 2. To provide power to the car's electrical equipment when the engine is off or at low idle. 3. The car battery acts as a voltage stabilizer for the entire electrical system. 4. The car battery stores excess electricity generated by the alternator.

[FinnDella]

I've encountered a similar situation before. When charging the battery, don't rush to start the engine. Attempting to crank the engine while the charger is connected can cause sparks that may ignite hydrogen gas emitted by the battery. I've seen someone do this and the explosion deformed their hood. Modern smart chargers do have overvoltage protection, but the instantaneous current surge of hundreds of amps during startup can fry the charging module. One winter when my car wouldn't start, I tried to turn the ignition while the charger was connected, and the entire dashboard went dark. Later inspection revealed both the fuse and the charger's circuit board were completely burnt out. The safe and worry-free approach is to patiently charge for at least two hours before attempting to start.

[AidenAnn]

Having repaired cars for over a decade, what I fear most is owners forcibly starting the engine while the battery is charging. A charging battery is like a gas cylinder, with its electrolyte producing large amounts of flammable gas. At this moment, the spark from the ignition switch is equivalent to an open flame. One Mercedes-Benz S-Class customer burned out the entire generator winding because of this, costing over thirty thousand in repairs. In reality, when the battery is completely dead, the charger's power can't support the starting current, only adding risk. The correct approach is to disconnect the charging cable, let it sit for half an hour to allow the gas to dissipate, and then attempt to start.

[TaliaLynn]

As a circuit engineer, let me explain the principle: During charging, the voltage across the battery terminals can reach as high as 15V, while during vehicle startup, the starter motor instantly pulls the voltage down below 9V. Such drastic voltage fluctuations may cause the charger to misjudge and trigger protection mechanisms, leading to system failure. Last year, during actual testing of a certain German car model, attempting to start the engine while charging directly burned through the power management chip of the onboard computer. It is recommended to either disconnect the negative terminal clamp during charging or use a dedicated charger with isolation mode.