Which Terminal to Disconnect When Cutting Off Car Battery Power?
3 Answers
It is necessary to disconnect the negative terminal, not the positive one, and of course, there is no need to disconnect both terminals. Below is relevant information about the battery: 1. Battery: The battery, also known as a storage battery, is a device that converts chemical energy into electrical energy. The battery referred to here is a lead-acid battery, which is mainly made of lead and its oxides, with sulfuric acid solution as the electrolyte. The normal service life of a car battery varies from 1 to 8 years, largely depending on the vehicle's usage. 2. Battery Replacement: If the battery is dead, it is recommended to first measure the battery voltage. If using a multimeter for inspection, measure the battery voltage when starting the engine. You can first use a high-frequency discharge machine or a battery tester to measure. Under a load current of no less than 110 amps, the minimum voltage should not be lower than 9.6 volts and should remain stable for 5 seconds. If the voltage is below 9.6 volts but can remain stable for 5 seconds, it indicates over-discharge, and the battery should be recharged promptly. If the voltage is below 9.6 volts and cannot remain stable for 5 seconds, dropping rapidly to 0 volts or close to 0 volts, it suggests a possible battery fault that may require replacement.
I've replaced my car battery several times myself, always disconnecting the negative terminal - the one with the black cable. I remember the first time I tried doing this, I attempted to disconnect the positive terminal for convenience. As soon as I loosened the bolt, I saw sparks flash, which gave me quite a scare. Later, I consulted an experienced mechanic and learned that all the metal parts of the car body are grounded. If your tool accidentally touches the car body while disconnecting the positive terminal, it can cause a short circuit. At best, this might create sparks and damage electrical components; at worst, it could fry the battery. That's why disconnecting the negative terminal is safer - without completing the circuit, there's no risk. Before disconnecting, make sure the engine is completely off, and that no accessories like the radio or lights are on. Wearing insulated gloves during the operation is also a wise precaution. Since adopting these habits, I've never had any issues with battery maintenance.
If you want to DIY a car battery disconnect at home, I recommend directly disconnecting the negative terminal—the small post connected to that black cable. Why choose this? The car body itself serves as a grounding system. If you touch the positive terminal first, any tool coming into contact with metal parts can easily cause a short circuit, sparking not only damage to the battery but also harm to the electronic control unit. Here’s how I usually do it when working on my car: turn off the engine, remove the key, make sure all electrical devices are off, then use a wrench to slowly loosen the negative clamp—just a gentle push to disconnect. The whole process takes just two to three minutes, safe and hassle-free. Don’t forget to check the battery terminals for cleanliness after disconnecting; clean off any oxidation to extend the battery’s lifespan.
