Why You Should Never Keep Power On when Replacing a Car Battery

Every 3 to 5 years you need to end up replacing the battery in your cars but a question we get very often is whether to keep power to the vehicle when replacing the battery. Car owners often use a jump box, another car, or a battery-saver device to keep the car powered up while replacing the battery which is very risky and dangerous and may end up being a very expensive lesson if you do the same. Because the risks of keeping power to the car outweigh the risks of disconnecting the battery, at the YOUCANIC garage we never keep the power on when replacing a car battery. In the following video, we go over why it is important to disconnect the battery completely and not back-feed the vehicle when replacing a car battery.

Why Keeping Power to Car Battery is Too Risky

The crux of the issue lies in the potential for damage to the car’s intricate electrical and electronic systems. Let’s explore this in detail:

Damage to Vehicle Electronics

Modern cars are intricate machines with complex electrical systems and computers. The vehicle’s ECU (Electronic Control Unit), infotainment system, and various sensors are particularly sensitive to power fluctuations. During a battery replacement, a sudden surge or drop in power can occur. If power is maintained throughout the process, this fluctuation could potentially harm these sensitive electronics. Moreover, voltage spikes or electrical shorts may occur, leading to additional unforeseen problems.

Another common and major problem with keeping power to the car when replacing the battery is that you may accidentally short the battery-positive terminal to the ground of the vehicle. This can be a very expensive repair as at minimum it will blow a 50A fuse but in many cases, it may damage the Engine Control Unit which can range between $1000 and $3000 on a modern vehicle.

Airbag Light On

Replacing a car battery while keeping power on can, in some circumstances, trigger the airbag warning light or even worse, lead to unintended airbag deployment. The airbag system in your car is designed to be highly sensitive and responsive, and an unexpected power fluctuation might trigger it. In order to reset the warning light, a full system scan would be required using a specialized tool like the YOUCANIC scanner.

The Loss of Car Settings: A Manageable Inconvenience

Many car owners worry about losing certain settings when the battery is disconnected. While it’s true that certain features may need to be resynced, and transmission and engine adaptation values may be lost, none of these settings are important or needed. In fact, having the ECU reset sometimes is a good thing because the ECU and Transmission Control Module shift points get corrupted over time and a reset makes your car shift even better. While the window and sunroof one-touch close/open setting may be lost it’s important to remember that these are typically simple procedures that won’t affect the overall functioning of the car and don’t require removal of any parts.

It is simply not worth the risk to change the battery while the engine is running. Always turn off the engine before you disconnect the battery.

Traction Control Light On

When you disconnect the battery to replace it, after you reconnect the new battery you will notice ABS and traction control on in your dashboard. Those are easy to reset. Simply start the engine, turn the steering wheel full left then full right and repeat a couple of times. On some cars, you need to drive for a couple of minutes, and the ABS, and traction control lights reset automatically.

On the other end, if you decided to keep power to the car and the airbag light gets triggered due to a low voltage issue, you will need a professional-level scanner such as a YOUCANIC scanner to clear the airbag light. To avoid triggering the airbag or SRS light, simply disconnect all power from the vehicle when replacing the battery.

Windows Synchronization

For instance, your car’s one-touch window feature might need resyncing after a battery replacement. To restore it, you must press and hold the window switch in both the up and down positions for a few extra seconds. The process is similar for resyncing sunroofs if your car has one.

Radio Code

Moreover, you may need to re-enter your radio code after the battery replacement. Though it may take a few extra minutes, it’s a relatively minor inconvenience and typically the radio code can be found in the car’s manual or obtained from the manufacturer. Also, there are a lot of services online where you can go and purchase the radio code for your car for under $10. Just do a search and you will find someone that will be willing to give you the radio code of your car if you send them the serial number of the radio.

Conclusion

At the end of the day, maintaining power during a battery replacement involves a risk-benefit analysis. On the one hand, it might save you a few minutes by keeping certain features of your car intact. However, the potential hazards outweigh the benefits, making it a risky endeavor.

The potential cost of damage to the electronic systems, or a triggered airbag, would far exceed the minor inconvenience of resyncing a few features or entering a radio code. Besides those basic settings, there is no other valuable information that is saved by keeping the car back fed with another jump box or jumper cables. Therefore, the best course of action is to disconnect the power when replacing the battery and take the necessary steps afterward to resync and reset any features that may have been affected.

We believe that understanding your vehicle, its intricate mechanisms, and maintenance requirements is fundamental to being a responsible car owner. We hope this detailed overview helps you make informed decisions when it comes to car battery replacements. Let’s continue to learn together and ensure that we make car maintenance as safe and efficient as possible.

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