Disconnecting the battery during repairs is a pretty standard procedure regardless of the type of issue you’re dealing with.
Along with this protocol, disconnecting the negative terminal first before the positive terminal is a must.
But what’s the reason behind this practice?
The negative battery terminal, also known as the ground strap or cable, is directly connected to the vehicle’s engine, body, and chassis. The positive terminal is connected to the starter, the alternator, and the fuse boxes.
Removing the positive terminal without removing the negative terminal can create a situation where a tool that is touching the engine or body can still short out against the positive battery terminal. While this isn’t likely to happen, it’s still a good idea to remove the negative terminal, even if only one of the two terminals is being disconnected.
If you’re just going to remove one terminal, remove the negative terminal rather than the positive terminal.
Removing the positive battery terminal without removing the negative terminal can create a situation where a tool that is touching the engine or body can still short out against the positive battery terminal. While this isn’t likely to happen, it’s still a good idea to remove the negative terminal, even if only one of the two terminals is being disconnected.
–Richard McCuistian, ASE Certified Master Automobile Technician
If you’re just going to remove one terminal, remove the negative terminal rather than the positive terminal.
Here are other problems that can arise when you fail to disconnect the car battery’s negative terminal first:
It’s best to disconnect your vehicle’s battery in the following situations:
When disconnecting a car battery, it’s always important to make sure that the engine is turned off. Attempting to remove a battery while the engine is on can spike sensitive electronics and cause a lot of damage.
The next step is to locate the battery. Most vehicles have it under the hood, while some have it under the trunk. Always consult your owner’s manual to determine the right location.
The next step is to locate the battery terminals. The negative terminal is usually denoted by a “-” symbol, while the positive terminal has a “+” symbol. In most cases, the positive terminal also comes with a red plastic cover.
A black battery cable connects to the negative terminal, while a red cable connects to the red positive terminal, signifying its hazardous nature.
Before you go any further, you should know the answer to the question, “Which battery cable do you take off first?” Using a wrench, loosen the nut on the negative terminal and take it off the battery post. Make sure that the cable isn’t anywhere near the terminals. Then, proceed with removing the nut on the positive terminal.
Dead batteries aren’t always a lost cause. In some cases, you only need to recharge them to get them up and running. Here’s the right way to charge your car’s battery.
Step 1: Determine the charge rate. This is usually based on the state of charge (SOC) and charging rate.
Step 2: Connect the charger to the battery, but make sure that the charger isn’t plugged in yet.
Step 3: Set the charging rate. The initial charge rate should be about 35A for 30 minutes to kickstart the charging process.
Keep in mind that charging a battery too fast can increase its temperature at a rapid rate, warping the plates in the process.
Note: Never charge or jump-start a frozen battery. A car battery can freeze up in its discharged state because the electrolyte turns into water.
A frozen battery often bulges at the sides because of water expansion. As a result, the gas pockets in the battery can explode.
Once you’ve recharged or gotten a replacement battery, here’s how you can reconnect it:
When disconnecting the battery, there’s much more to consider than which battery cable to take off first.
Disconnecting the car battery can erase important information from your vehicle’s computer. While some might not be important, losing data like adaptive fuel calculations and system diagnostics tracking can cause issues when you restart your car.
In some cases, disconnecting a battery without a backup power or memory saver can cause the following issues:
To prevent these problems, connect your vehicle to a backup power supply before disconnecting the battery. You can also use a memory saver that either clamps onto the battery terminals or plugs into the cigarette lighter.
Most new car batteries are made with a maintenance-free design in mind. Still, it pays to keep an eye out for your battery’s condition to avoid unwanted repairs down the road.
Battery maintenance includes a thorough inspection of the electrolyte level. If the electrolyte level is low, most manufacturers recommend adding a bit of distilled water.
Proper battery maintenance also involves making sure that the battery terminals are free from corrosion, the battery case is clean, and the hold-downs are secured.
Check for loose or corroded connections at the battery terminals or the ground connector on the engine block.
If you have loose or corroded connectors, clean them using a tablespoon of baking soda mixed with a liter of water. Brush the mixture onto the battery and housing to neutralize the acid.
Then, you can proceed with cleaning the connections and washing the area with water.
Also, make sure that the battery hold-downs are secured enough to prevent the battery from moving, but not tight enough to cause the case to crack.
You can try to extend the service life of your car’s battery all you want, but there will come a time when you’ll need to replace it with a new one.
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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.