Why Is Your Disconnected Car Battery Losing Voltage

If you want to know why your disconnected car battery is losing voltage, then you’ve found the right article! In this article, not only will you find out why this is happening, but you’ll also learn how you can reduce the rate of discharge and stop it from happening altogether!

So keep reading to find out everything you need to know!

Will A Disconnected Battery Discharge?

A disconnected battery will discharge at about 5-15% a month, depending on the quality of the battery. This is because of the self-discharge rate. This means that if the battery is not connected to a charging source, it will slowly lose power. To avoid this, connect your battery either to a trickle charger or a maintainer, which will keep the charge level steady and prevent any discharge while not in use.

What Happens If You Leave Your Car Battery Disconnected?

Leaving your car battery disconnected can cause a variety of issues. The most common issue is the self-discharge rate, which means that the battery will slowly lose power over time without being connected to a charging source. This could lead to problems starting your engine or running electrical components when you do eventually connect it back up.

Why Do Batteries Self Discharge When Disconnected?

Batteries self-discharge when disconnected due to the chemical reactions that take place inside the battery.

As these reactions take place, energy is lost in the form of heat and electrical current, which gradually reduces the charge level of the battery.

This is why it’s important to keep your battery connected to a charging source if you plan on not using it for an extended period. This will ensure that the battery remains at an optimal charge level and is ready to be used when you need it.

The rate of self-discharge also depends on the type and quality of the battery, with some batteries draining faster than others. Generally speaking, good-quality batteries have a much lower self-discharge rate compared to cheaper alternatives.

Can A Battery Drain With The Negative Cable Disconnect?

Yes, a battery can still drain with the negative cable disconnected. This is because of the self-discharge rate of the battery. Even when not connected to a charger or power source, the battery will slowly lose power over time. However, a battery will self-discharge slower when the negative cable is disconnected compared to when the battery stays connected.

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How Long Can You Leave A Car Battery Disconnected?

If your car battery has been stored properly and securely, it can last up to 6 months! However, generally, it’s not advised to leave it for more than two weeks without at least trickle-charging it. This is to ensure that the battery does not lose a significant amount of charge due to self-discharge.

If you will be leaving your car disconnected for longer than two weeks, it is best to disconnect the negative terminal and store the battery in a cool, dry place. This will help prevent any further losses in power while disconnected. Additionally, it’s also a good idea to connect the battery to a trickle charger every few months if it will be disconnected for longer than two weeks. This will ensure that your battery remains in peak condition and keeps its maximum capacity.

Leaving A Car Battery Disconnected Overnight

Leaving a car battery disconnected overnight can be good for some of the electrical systems, like the clock and computer systems. This is because they can draw a small amount of power from the battery, even when it is disconnected.

However, if the battery will be disconnected for more than one night, it is best to connect it to a trickle charger that can keep up with its self-discharge rate. This will help to ensure that the battery remains in peak condition and has enough charge when you reconnect it; additionally, if the car’s computer systems are connected.


Leaving a car battery disconnected for too long can reduce the charge level and cause starting problems. Batteries self-discharge over time due to chemical reactions taking place inside, with some batteries draining faster than others.

It is best to connect the battery back up to a trickle charger or maintainer if it will be left disconnected for more than 2 weeks. Leaving a battery disconnected overnight is generally fine for most vehicles, but it’s important to keep in mind that the battery can still lose some charge due to its self-discharge rate.

Overall, it’s best to ensure you keep your car battery properly maintained and charged when not in use. This will help protect the life of the battery and ensure it starts when you need it to.

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