Why You Should Never Keep Power On when Replacing a Car Battery
Every three to five years, you need to replace the battery in your car, but we are often asked whether one should keep power to the vehicle when replacing the battery or not. Car owners often use a jump box, another car, or a battery-saver device to keep the vehicle powered up while replacing the battery, which is risky 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 main issue lies in the potential damage to the car’s complex 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. A sudden surge or drop in power can occur during a battery replacement. This fluctuation could potentially harm these sensitive electronics if power is maintained throughout the process. Moreover, voltage spikes or electrical shorts may occur, leading to additional unforeseen problems.
Another common problem with keeping power to the car when replacing the battery is that you may accidentally short the battery’s positive terminal to the vehicle’s ground. This can be a costly repair as, at minimum, it will blow a 50A fuse, but in most cases, it will damage the Engine Control Unit, which can cost between $1000 and $3000 to replace on a modern vehicle.
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Airbag Light On
In some circumstances, replacing a car battery while keeping the power on can trigger the airbag warning light or, even worse, lead to unintended airbag deployment. Your car’s airbag system is designed to be highly sensitive and responsive, and an unexpected power fluctuation might trigger it. A full system scan using a specialized tool like the YOUCANIC scanner would be needed to reset the warning light.
What happens if you disconnect the battery?
Disconnecting your car from its source of electricity might sound like a bad idea, but in reality, most problems that arise during a proper battery change are only slight annoyances.
The Loss of Car Settings: A Manageable Inconvenience
Many car owners worry about losing certain settings when the battery is disconnected. While it is true that certain features may need to be resynced, and transmission and engine adaptation values may be lost, none of these settings are essential to the overall health of the vehicle. Having the ECU reset sometimes is good because the ECU and Transmission Control Module shift points can become corrupted over time, and a reset makes your car shift even better. While the window and sunroof of a one-touch close/open setting may be lost, it is important to remember that these are typically basic features that will not affect the overall functionality of the car and do not require the removal of any parts.
Changing the battery while the engine is running is not worth the risk. Always turn off the engine before you disconnect the battery.
Traction Control Light On
When you disconnect the battery to replace it, you will notice ABS and traction control warning lights in your dashboard after reconnecting the new battery. Those are easy to reset. Start the engine, turn the steering wheel fully to the left, then fully to the right. Repeat this a couple of times. Then, you need to drive for a few minutes. On some cars, the ABS and traction control lights reset automatically.
Conversely, if you decide to keep power to the car and the airbag light is triggered due to low voltage, you will need a professional-level scanner, such as the YOUCANIC scanner, to clear the airbag light. Disconnect all power from the vehicle when replacing the battery to avoid triggering the airbag or SRS light.
Windows Synchronization
Your car’s one-touch window feature might need to be resynched 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
You may also need to re-enter your radio code after a 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. There are also a lot of services online where you can purchase the radio code for your car for under $10. Just search, and you will find someone willing to give you the radio code of your car if you send them the radio’s serial number.
Conclusion
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 risky.
The potential cost of damage to the electronic systems or a triggered airbag warning light far exceeds the minor inconvenience of resyncing a few basic features or entering a radio code. Besides those basic settings, keeping the car backed with another jump box or jumper cables saves no other valuable information. 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.
Understanding your vehicle’s intricate mechanisms and maintenance requirements is fundamental to being a responsible car owner. We hope this detailed overview helps you make informed decisions regarding car battery replacements. Let’s continue to learn together and ensure we make car maintenance as safe and efficient as possible.
Frequently Asked Questions
What happens if you change a car battery without a memory saver?
Nothing bad. You lose the window one-touch setting, radio code, and driver adaptation data, but those are not critical, and it is safer to disconnect the battery than keep the power on.
What should I do after installing a new battery in my car?
All you have to do is sync the windows and sunroof and enter the radio code.
