Should the power cables be disconnected when charging a car battery?

[LaJoy]

It is recommended to disconnect the power cables when charging a car battery, because the car's electrical circuits remain active even after the vehicle is turned off and locked. For instance, the control circuits for the car doors continue to operate - when using the remote key to lock/unlock the vehicle, the doors will automatically open/close. Therefore, if you connect an external charger to the battery without removing it from the vehicle, it may potentially damage the remote door control system. The principle of car battery charging: The charger's voltage must be higher than the battery's voltage to enable charging. The greater the electromotive force difference between them, the faster the charging speed and the larger the charging current. Typically, a 24V charger has a maximum (no-load) voltage of 28V, with 60A indicating its maximum output capacity. When charging, the charger is under load, at which point the voltage becomes the actual charging voltage of the battery, with 40A representing the charging current. This current will gradually decrease as the charging process completes. Additionally, the charging current magnitude also relates to the battery's capacity size.

[Angelo]

I've always believed that when charging a car battery, it's essential to remove the power cables, especially the negative terminal, to avoid the risk of short circuits. If the cables aren't removed, current may flow through the vehicle's circuitry during charging, potentially causing sparks or damaging electronic components like the onboard computer. The procedure is straightforward: first, turn off the engine and all electrical devices, use a wrench to loosen the negative terminal clamp, move the cable aside, and then connect the charger. After charging, disconnect the charger before reattaching the negative cable. I once saw a friend skip this step to save time, only to end up blowing a fuse and spending hundreds on repairs. Developing this habit not only protects the battery's lifespan but also prevents accidents. Remember, this is even more crucial for new cars or those with anti-theft systems—safety always outweighs convenience.

[RemingtonLee]

I think whether to disconnect the power cable depends on the situation. If you don't disconnect it, quick charging can be safer in certain environments, such as ensuring no risk of sparks or high humidity, which might save some temporary hassle. However, it's best to disconnect the negative terminal to prevent potential short circuits and component damage in case of poor charger contact. I drive an old car myself and have occasionally charged without disconnecting the cable without issues, but that's because I checked the battery was in good condition. Generally, it's advised not to cut corners—spending a few minutes to remove the negative terminal can reduce risks and extend battery life. Especially when the battery is aging, disconnecting the cable is even more important to avoid minor issues turning into major repairs. A simple habit can bring great peace of mind—try making it a routine.

[LaAaliyah]

From a professional perspective, the negative battery cable should be disconnected when charging a car battery. This is because charging without disconnection allows current to circulate through the body circuit, potentially causing voltage fluctuations that could damage electronic components such as the ECU or sensors. The standard procedure is: after turning off the engine and cutting power, loosen and remove the negative terminal clamp, then reconnect it after charging is complete. This not only protects the battery from overheating or explosion risks but also safeguards the vehicle's overall electrical system. The operation is simple and can be performed by anyone.