Can a battery drain with the negative cable disconnected?

Asked By: Chegdali Planellas | Last Updated: 23rd March, 2020
Category: automotive road side assistance
4.8/5 (6,363 Views . 28 Votes)
No, it won't drain overnight if you disconnect the positive lead. However, it's very bad practice & can be dangerous, assuming the car is negative earth/ground. NB: Just about every car built since about 1965 is negative Earth. Disconnect the negative terminal.

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Also, can you just disconnect the negative terminal?

When you are finished with the work on your vehicle, you will need to reattach the negative battery terminal to the battery. Disconnecting a negative battery terminal is an easy task, but you are working around a battery. Batteries contain acid and can cause injury if proper safety precautions are not taken.

Additionally, what happens when you disconnect the negative battery cable? By removing the negative battery cable you are disconnecting the battery from the chassis of your vehicle. If you begin to remove the positive side before the negative and your wrench would make contact with any part of the vehicle, then you could cause a short in the system.

People also ask, is it OK to leave car battery disconnected?

When you disconnect your car battery from the car, it helps prevent the electrical systems including the clock and on-board computer system from draining it completely. Therefore, if you leave the car battery unattended for longer period, then it might damage the battery and even need replacement.

How long will a car battery last if disconnected?

3 months

34 Related Question Answers Found

What happens if you connect the negative terminal first?

The negative cable is connected to the body/chassis of the car. If you connect the negative first, then the positive, if you happen to touch the wrench to something metal while it is touching the positive terminal, that's a short - because the chassis is already connected to the negative battery terminal.

Which terminal do you connect first?

Safety: Always remove the negative cable first, then the positive cable. When you connect the battery, connect the positive end first. Here is the order: Remove black, remove red, attach red, attach black. Ensure that the connections on both end are secure by trying to move the battery around.

How long does battery need to be disconnected to reset ECU?

It's a real tight fit, but if you can find it and disconnect it, leave it disconnected for 30 seconds. The nice thing about this method over the "disconnect the negative cable" method is that you don't have to reprogram your radio! If you can't find it, then do the negative cable - again for about 30 seconds.

Will disconnecting the positive battery cable?

Never disconnect a battery cable when the engine is running. If the tool touches the battery positive terminal and a chassis ground simultaneously, as long as the negative battery cable is not connected, no damage will occur.

When installing a battery which cable do you connect first?


Always remove the negative cable first to avoid short circuiting the positive terminal. Once removed, disconnect the positive terminal using the same method and release the battery hold-down clamp with a wrench. Lift the DieHard battery up and out of the battery tray.

Do car batteries drain when not in use?

Batteries have a natural self discharge or internal chemical leakage; and today's cars draw a tiny amount of power from the battery when not in use to keep all the electrical systems 'alive'. Over time, the battery will become fully discharged if not driven.

Do I have to disconnect both battery terminals?

I recommend disconnecting both terminals. But if only one terminal is disconnected, then it should be the negative terminal. There is only one reason for this. Because the negative end of the battery is connected to ground.

How long do you disconnect a car battery to reset computer?

How to Disconnect a Car Battery to Reset the Computer
  1. Clean any corrosion off of the battery and terminals with a can of spray-on battery cleaner.
  2. Hold the positive and negative cable ends together so they're touching each other but not the battery.
  3. Wait five minutes for the diagnostic information to be erased.

Can I reset my car's computer by disconnecting the battery?


An old mechanic's trick for turning for temporarily eliminating certain kinds of driveability problems is to disconnect the battery ground cable for 10 seconds to "reset" the computer. Essentially, this trick erases the stored fault codes in the PCM's keep alive memory and turns the Check Engine light off.

How do I stop my car battery from discharging?

5 Ways to Help Avoid a Dead Car Battery During the Summer
  1. Keep it cool. Since heat drains a car's battery, parking it in a cool or shaded spot can buy your battery extra time.
  2. Increase your driving time.
  3. Cut down on car battery drain.
  4. Keep it clean.
  5. Get a car battery charger.

How many years do car batteries last?

Under these conditions, you can probably expect your car battery life to be about six years. On average, a car battery lasts between two and five years. If you live in the northern United States, your car battery lifespan will be longer, because you're in a cold climate.

How long can you leave car without starting?

There is no particular time span to keep an engine off. Modern cars doesn't have any issue in keeping idle. Car maintenance is the key fact. In my opinion warm up once at least every two weeks, if possible, start the car every two weeks and drive it for about 15 minutes.

Which battery terminal must be disconnected first and why?


You should always remove the negative battery terminal first, to reduce the risk of sparks which can make the car battery to explode. Once the negative terminal has been located, use the wrench to loosen the nut that holds the terminal.

What happens when you connect wrong battery terminals?

During the process of charging the battery, you may accidentally mix up the cables and put the wrong one on the incorrect terminal. When this happens, it could damage the battery as well as other associated electrical components. If you reverse the polarity of the charger to the battery, the battery may explode.

What happens if you connect car battery backwards?

When a car battery is connected backward a fuse designed to protect vehicle electronics should blow. It is not common to damage the Engine Control Unit / Module by connecting the battery cables incorrectly. Most of them are designed to withstand reverse polarity.