Can A Battery Drain With The Negative Cable Disconnected?

  • Disconnecting the battery des help the battery discharge less, but it does not stop it from self-discharging.
  • It has to be kept in mind that you should always disconnect the negative wire as it is safer.
  • There are other steps that you might take in order to make your battery charge last longer.

Often times if the battery is connected on both terminals, the battery might drain out even if the equipment is not used. This is a common issue all batteries have and all users suffer from. So, this begs the question, can a battery drain with the negative cable disconnected?

With the negative cable detached, a car battery would “self-discharge” at a rate of 5 to 15 percent each month, which is the best option for long-term parking if you can’t link it up to a charger. Leaving the battery connected for a week will deplete it by 20% or more.

Other important issues about removing the negative cable may arise, such as its benefits and drawbacks, how it affects the batteries, and so on. I’ll attempt to address some of the most common queries and provide extensive and detailed answers throughout this article.

Why Does a Car Battery Lose Charge Even When the Negative Cable Is Disconnected?

Simply unplugging the negative wire will not prevent your batteries from losing charge, as I previously stated. Don’t get me wrong: it’s certainly better than nothing, and it’ll help to keep your battery charged while you’re away.

Self-discharge is a process that every battery goes through. You’ve undoubtedly seen it when you buy a pack of AA batteries and it says something along the lines of “Will hold 90% of its charge after 5 years.”

But where did the 10% go if you weren’t using the battery for those 5 years? How can a battery drain with the negative cable disconnected?

Self-discharge is the answer.

Self-discharge occurs when a battery is not connected to a smart charger in float mode, which effectively keeps it at a perfect 100 percent charge.

Self-discharge indicates that your battery is chemically returning from a state of charge to a state of discharge since it is technically easier for the battery’s chemistry to do so and it is where it naturally wants to be.

The pace at which your battery accomplishes this is determined by the sort of battery you have, and automobile starting batteries are classified as lead-acid batteries (whether sealed or flooded).

When not in use or connected to anything, healthy lead-acid batteries will self-discharge at a rate of 4-5 percent each week.

The circuit is no longer complete when the negative terminal is disconnected and just the positive terminal is attached.

That is correct.

If you keep both wires connected, your automobile will most certainly die in 2 to 4 weeks due to “parasitic draw.”

All of the computer systems in contemporary automobiles that suck energy from your battery even when your car is switched off are known as parasitic draw.

Even when your car is turned off, things like your anti-theft system, clock radio presets, and more steadily eat away at the battery to preserve their settings.

How Does Sulfation Affect Battery Charge?

The problematic aspect about losing your charge that will eventually catch up with you is that when a battery enters a state of discharge, it instantly begins to sulfate, and the farther you go into a state of depletion, the faster it will sulfate.

Sulfation occurs when the chemical processes that occur during discharge cover the lead plates within your battery with sulfates (a white coating).

This sulfation coating is mild at first, but it may be peeled off your battery plates by recharging if treated quickly. Deep-cycle batteries have a more forgiving protective alloy on the plates, whereas automobile starting batteries can be irreversibly damaged to some degree whether or not they are recharged quickly. That’s why automobile batteries can only be deep-discharged a dozen times before they lose their charge, but deep-cycle batteries can be deep-discharged hundreds of times.

However, if a battery is left in a discharged state for an extended period of time, the sulfation hardens into a crystalline state, making it virtually impossible to remove from the lead plates – especially in automobile starting batteries.

These sulfate crystals raise your battery’s internal resistance, making it more difficult to charge it and bring it to a full charge, as well as making your battery less effective at releasing electricity when it’s needed.

Each time you drain the battery, sulfates pile up to the point where they can either bridge the space between the plates, causing an internal short and killing the battery, or they can simply cover the plates sufficiently to leave the battery useless.

How to Properly Disconnect a Car Battery Cable?

These methods will assist you if you have never attempted to detach a battery previously. It’s easy to do and just takes a few tools.

However, you must know how to do it correctly to assure your safety and that nothing goes wrong with your vehicle’s electrical system. If you follow these procedures, the procedure will run easily and swiftly.

Step 1: Locate the Battery

They’re usually fastened in place beneath the hood of most automobiles. You’ll have to do something about it.

Check your owner’s handbook if you’ve never lifted the hood of your car before. It will show you how to do it and where the safety catch is located beneath the hood’s front.

The batteries in some automobiles are hidden in the trunk, out of sight. If your battery isn’t beneath the hood, it’s almost certainly in the back of the car. To be sure, see your owner’s handbook.

Step 2: Locating Both the Positive and Negative Terminals

One of the most crucial phases is this one. The positive terminal is denoted by a “+,” whereas the negative terminal is denoted by a “-“.

Some batteries have plastic caps over the terminals that must be removed in order to access the battery cables (the wires that link the battery to the rest of the car) and the cable clamps that must be removed in order to detach the battery.

Step 3: Finding the Right Wrenches

Depending on how much room there is to maneuver the wrench and whether the battery cable utilizes a single bolt on the clamp or one that also uses a nut on the other end, you’ll only need a couple of wrenches to complete the task.

You’ll have to borrow or purchase a set of wrenches from a friend or cousin.

Because most, but not all, battery-cable clamps use 10-millimeter bolts, disconnecting the cables will almost certainly require a 10-millimeter open-end wrench.

A socket wrench set with the same-size socket will also come in handy. In certain circumstances, a simple adjustable open-end wrench can suffice.

Step 4: Unbolting the Connections

When dealing with batteries, it’s a good idea to use eye protection. To begin, unbolt the negative battery cable and lift it free to detach it. To get it off, you’ll have to wiggle and twist a little.

Never allow the wrench to come into contact with both the negative and positive terminals at the same time.

Even though the battery is technically dead, there may be enough residual power in it to cause it to short out and ignite, and you don’t want any sparks near the battery or in the engine compartment.

There’s also a chance that shorting out the battery in this manner would harm your car’s electrical system or engine-control computer. Push the negative cable out of the way once you’ve removed it.


In this article I have explained in detail the effect that disconnecting the negative battery cable might have on a car battery, as well as other factors that a battery might be affected by.

So, the question in discussion, “can a battery drain with the negative cable disconnected”, can be said to have been answered thoroughly in this article. Hope this helped you understand the ins and outs of the topic.

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