Planning to Change the Car Battery while the Engine is running? Read this First

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Most times, dead or aging car batteries can be replaced without any incident so much so that it’s likely that there’ll be no worry on your part if someone told you they’re going to change the battery.

Don’t take it for granted though, there are always risks associated with battery swaps, especially if not done carefully.

One such risk that some mechanics take is to disconnect and replace the car battery while the engine is running.

This is usually done to prevent the car from losing its memory settings when the battery is removed.

So, this post explains the dangers the car is exposed to when the battery is changed while the engine is still running and also provides tips that you can use to avoid losing the memory settings of the radio and car computer.

Quick Tip: Do not disconnect the car battery while the car engine is still running. Doing so risks damage to the car’s electrical systems.

Read on to learn why you should switch off the engine first.

Why You Shouldn’t Change the Car Battery with the Engine still Running

Disconnecting and removing the car battery with the engine still running can result (not always) in harmful voltage spikes from the alternator damaging not only the alternator (diodes) but also the car computer.

And then there are the additional and potentially costly repairs that you incur to fix the damage.

The likelihood of short-circuits and arcing increases with the engine running as the disconnected cables are still energized (battery positive) which can damage the alternator and the car body (arcs).

You may also be interested in this post: How long a car battery lasts when disconnected

Do this Instead |How to Safely Replace a Car battery

You can follow the steps below to safely disconnect and reconnect the car battery.

Note: Make sure the car engine is switched off

#1. First, disconnect the negative terminal (with the black cable usually) from the battery post (marked – sign)

#2. Next, disconnect the positive terminal (with the negative cable) from the battery post (marked with a + sign)

#1. To safely reconnect the battery, first, connect the positive terminal (with the negative cable) from the battery post (marked with a + sign).

#2. Next, connect the egative terminal (with the black cable usually) from the battery

You can then start the engine. Some cars may initially run rough or the idle RPMs may initially be as low as 500 for a few minutes as the car computer relearns the ideal settings for your car before it stabilizes to the original settings.

How to Keep the Car Memory Intact when Replacing the Battery

Worried about losing the memory settings of the car computer and radio, then follow either of these steps.

# 1. Use a trickle charger

You may be able to stop the car radio from losing its memory settings by first connecting the battery terminals to a car trickle charger (with the battery still connected).

Next, disconnect the old battery (while the trickle charger keeps the car electronics powered and their memory settings intact).

Lastly, connect the new battery securely (make sure you do not reverse the terminals) and then remove the trickle charger connections.

Hope this little trick saves you time that you’d otherwise spend programming your car radios stations and other settings. Thanks, @Selinger from RA4 World.

# 2. Use a car battery memory saver

Alternatively, you can also use a memory saver. It has a cigarette lighter plug and supplies power to keep the memory settings intact when you replace the car batteries.

You may also be interested in this post: How long the car battery lasts with the radio on?

Related Questions

# 1. Can a Car Engine Run without a Battery?

Yes, the car engine can continue running without a battery connected provided the alternator is running, in good condition and able to supply enough power for the car’s electrical system.

Note: This is not recommended. Always switch off the car engine first before removing the car battery.

#2. Can You Change a Car Battery while the Engine Running

Yes, you can change and replace a car battery with the engine running though this is not advisable because of the possible dangers associated with it.

Final Word

Avoid changing the car battery while the car engine is running. Doing so can damage the alternator and or other electrical components in the car.

If you are planning to do this because you want to avoid using the computer and car radio settings, use a memory saver to preserve the computer and radio settings instead.

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