What to Do After Replacing a Car Battery

  • November 15, 2023
Man Holding Car Battery Man Holding Car Battery

So, you’ve chosen the best battery, installed it in your car, and are ready to hit the road. Your ride is feeling fresh, and that engine is begging for a spin. But before you put the pedal to the metal, there are a few important post-battery replacement steps you need to take to ensure everything is running smoothly. 

Oh, and if you haven’t installed your battery yet and are looking for advice, we have you covered too. Read on to learn how to change a car battery the right way, how to prevent losing your vehicle’s settings, and what to do after installing a new car battery. 

How to Change a Car Battery Without Losing Settings

You might already have an idea of how to change a car battery. Just disconnect the battery terminals, remove the old battery, and reconnect the terminals to the new one, right? That’s certainly part of the process, but there’s more to car batteries than you might expect

If your vehicle loses power during a battery change, you could accidentally reset some important vehicle settings like:

  • Adaptive electronic control unit (ECU) memory
  • Automatic window controls
  • Car radio codes\
  • Radio presets and clock

If you’ve already replaced your battery and lost any of those settings, don’t panic —  we’ll explain how to restore them later in this guide. Here’s how to replace your battery without losing those precious settings: 

1. Use a Battery Memory Saver

What’s a battery memory saver, you ask? A battery memory saver (we’ll call it a BMS from here on out) is a device that maintains power levels in your vehicle during a battery change. That way, all of your important devices — primarily your ECU and radio — stay juiced up and retain their memory. 

Battery memory savers come in many different forms. Older ones take a 9V battery and connect to your vehicle’s cigarette lighter. Newer ones generally connect to your vehicle’s onboard diagnostics (OBDII) port and provide their own power supply. Some will need to be connected to another power supply, such as another battery. If you’re not sure which one you need, we recommend springing for the BMS that produces its own power supply, since older BMSs may not work on all newer vehicles. 

You’ll want to make sure that the BMS is properly hooked up before you disconnect your battery. Once you have, you’re free to proceed to the next step — disconnecting the battery cables. 

2. Locate Your Battery and Disconnect Your Battery Cables

First, locate your battery. It can generally be found offset to one side of your engine bay or trunk. It may also be hidden underneath a plastic panel or battery cover. In some vehicles, you may also find it located under the rear seat. Have a look around to find yours.

When you’re ready to disconnect your cables, loosen the nuts on your battery cables with a wrench or socket of the appropriate size. For modern vehicles, that size will likely be 10 or 12 mm. For classics, it’s probably 7/16 or 1/2 inch. 

Once the nuts are loosened, pull off the negative cable first (the black one connected to the “-” post). Then, remove the positive cable (the red one connected to the “+” post). 

Please Note: If you’ve chosen to use a BMS to save your settings, know that your positive battery cable still has electricity coursing through it. So don’t grab the metal end of the wire and be careful not to rest your positive cable on anything metal in your engine bay or trunk. Doing so may shock you or short out the connection, leading to blown fuses or damaged electronics. If you’re not using a BMS, it’s still good practice to avoid anything metal. 

3. Remove the Old Battery and Install the New One

Loosen or remove your vehicle’s battery hold-down strap if it has one. Then, remove your old battery. Follow the steps above in reverse to install your new battery. Place your new battery in the battery tray and tighten the battery hold-down strap. Ensure that you connect the positive battery cable first, followed by the negative. If you used a BMS to save your vehicle’s settings, you should be good to drive! If you didn’t, read on to learn how to restore any potentially lost settings. 

Pro Tip: When you purchased your new battery, you likely paid what’s called a “core charge.” According to the Bureau of Automotive Repair, a core charge is a form of deposit held for the return of a used part. If you’d like to get that deposit back, bring your old battery to the store where you purchased your new battery. 

Should You Run Your Car After Installing a New Battery?

In most cases, you can drive normally after installing a new battery. It is rarely necessary to run your vehicle afterward. 

Do You Have to Reset the Car Computer After Replacing the Battery?

If you didn’t use a BMS to save your vehicle’s settings, there are quite a few computers you may need to reset. Though restoring your radio presets and clock may be intuitive, some systems, like the ones below, might not be so self-explanatory.

Resetting Automatic Windows

If you’ve noticed that your windows no longer roll all the way up or down with one click, you may need to reset your automatic windows. To do so, follow these general steps or visit your local Tires Plus to get your windows functioning again:

  1. Make sure your car’s ignition is in the “On” or “Run” position. This will provide electricity for your vehicle’s power windows.
  2. For windows that won’t roll down automatically, fully roll the window down. Without releasing the switch, continue holding the switch down for 10-15 seconds.
  3. For windows that won’t roll up automatically, pull up on the switch until the window is fully rolled up. Without releasing the switch, continue lifting up on it for 10-15 seconds. 
  4. Repeat this process for every window that is not operating properly.
  5. Enjoy your automatic windows!

Note: Manual processes don’t always work for every vehicle, and sometimes you will need a scan tool to reset automatic windows. 

Finding Your Car’s Radio Code

Though radio theft is not as common as it once was, some cars have a radio code as an anti-theft measure. This code prevents your radio from being used in another vehicle if it is stolen. 

Unfortunately, disconnecting your battery can trigger this anti-theft measure and cause your radio to display “Lock” or “Code.” If this happens, you’ll need to find your vehicle’s radio code and enter it before you can use your radio again. Check these locations to access your radio code:

  • The stereo or security chapter of your owner’s manual or vehicle handbook
  • The inside of your glove box
  • Your vehicle manufacturer's website

Once you’ve found your vehicle’s radio code, use the stereo’s numbered buttons (analog or digital) to enter it. When you have, you should be able to listen to your sweet, sweet tunes once again!

Pro Tip: If you’re locked out of your radio and can’t find your car’s radio code, you may need to have it unlocked by an authorized dealer. If you do, make sure you have the vehicle title and personal identification with you to prove that you own the vehicle. 

Regaining Your ECU’s Adaptive Memory: How Many Miles to Drive After Disconnecting Battery 

Believe it or not, your car is one smart cookie! As you drive, it learns how much fuel it needs to consume and how it should shift to be as efficient as possible. For low-mileage vehicles, these adjustments may be minor, but for high-mileage vehicles, they could be significant. This information is stored in your vehicle’s ECU and is often referred to as adaptive memory. 

When you disconnect your battery without a BMS, your ECU’s adaptive memory may be erased. If this happens, your vehicle could forget what its ideal shift points and air-fuel ratios are. This loss of information can lead to:

  • Rough idling
  • Poor acceleration
  • Reduced fuel efficiency

We know that sounds scary, but don’t sweat it too much! Fortunately, your car is a quick learner and all it needs to recalibrate is some driving time. In most cases, it only takes 10-15 miles for these symptoms to go away. However, even after those miles, it’s likely that the ECU hasn’t fully relearned your vehicle. So, if you need to bring your car in for a smog check, you’ll want to drive about 75-100 miles beforehand to reach peak efficiency. 

Want to be Positive Your Battery Has Been Installed Correctly?

If you want to be absolutely sure you've done everything correctly and your ride is in top condition, consider Tires Plus battery services. The experienced technicians at your local Tires Plus can double-check your installation and make sure your vehicle is ready for smooth and trouble-free driving. Schedule your appointment today, and enjoy peace of mind on the road!

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