How Long Will A Car Battery Stay Charged If Disconnected?

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Car batteries always depreciate on their own because of the spontaneous reactions that take place even when they are left alone without any use or interference from any quarters. The sulphuric acid used as the electrolyte will eventually begin to eat the lead plates and deposit lead sulfates on the internal cells.

Any battery needs two cycles of charging and discharging for it to last long. Consequently, when a battery sits for too long, without these two cycles taking place, the sulfate deposits on its lead plates will begin to solidify or harden. (Read Also: Can I Start Car With Battery Charger Attached)

When this trend is not reversed by charging the battery intermittently, it will eventually lead to the total destruction of the battery.

This is because when you charge an idle battery, you are in essence reducing the extent of sulfation in the battery through the conversion of sulfate particles attached to the lead plates into useful plate materials.

The issue now is, how long you can keep a car battery charged if it is disconnected. (Read Also: How Long To Keep Car Running After Battery Died?)

So How long will a car battery stay charged if disconnected? Well, this depends on a few factors which are: the integrity of the battery itself, environmental conditions like temperature, and how charged the battery was before the disconnection.

Temperature is important in this case because lead-acid car batteries tend to discharge faster in hot weather than in the cold. However, after putting all these factors into consideration, it has been known that a battery in good condition will last up to about two weeks or even more and still remain fully charged when disconnected from the vehicle. 

Table Of Contents

Does A Disconnected Car Battery Lose Charge?

Certainly, a disconnected car battery loses charge even though the loss may not start immediately after the disconnection, but it eventually still occurs.

When a car battery is disconnected, the acidic electrolyte will begin to eat or react with the lead plates in the various cells of the battery thereby producing lead sulfate which may ultimately harden or crystallize and thus reduce both the life span and charge or voltage of the battery.

Considering all these developments, it can be said that, yes, disconnected batteries lose charges eventually. However, where the battery is intermittently charged, the whole process of sulfation is reversed during charging which will enable the battery to retain its charges. (Read Also: Does Revving The Engine In Neutral Charge The Battery? Find Out)

Which Battery Terminal Must Be Disconnected First And Why?

As a general rule, always disconnect the black or negative terminal of the battery first before the positive or red terminal. This is done principally to ground the circuit and prevent sparking and also guard against any possible damage to battery components or vehicle electronics.

How Should I Disconnect Car Battery Terminal?

Basically, we are always required to connect the positive (+)  or red terminals of car batteries first before the negative (-) or black terminals. By extension, when disconnecting, we are required to disconnect the black or negative terminal first before the positive or red terminal. (Read Also: How To Recharge A Car Battery Unturned)

How Do You Keep A Car Battery From Dying When Not In Use?

When a car battery is not in use, the corrosive acid in it reacts with the metallic plates in its cells to produce a sulfate compound which generally causes a depreciation in the voltage of the battery. In extreme cases, where sulfation, as the process is commonly called, is allowed to continue unabated, the battery may be totally damaged.

Conversely, if you charge the battery periodically, at least once weekly, the process is often reversed and the sulfate so formed may even be beneficial to the battery. (Read Also: Will A Bad Battery Keep A Laptop From Turning On?)

In a nutshell, charging the battery periodically helps to prevent the battery from dying even when it is not in use for a long time, because the lead sulfate formed is constantly being degraded and rendered harmless.

Will Disconnecting Car Battery Harm Computer?

Disconnecting a car battery should not harm a computer if executed correctly. However, serious issues may arise if the disconnection is done wrongly.

To disconnect the car battery when a computer is being used should be done in such a way that the computer will not be affected and this is by disconnecting the negative terminal of the battery first before the positive and when connecting,  simply reverse the procedure.

What Happens If The Jumper Cables Are Reversed On A Battery?

Virtually every driver knows that a dead battery can be resuscitated by jump-starting it with a car that has a charged battery. However, this simple technique can become very dangerous if it is not executed properly by connecting the jumper cables badly.

Jumper cables are commonly misconnected via connecting the positive terminal of one battery to the negative terminal of the other. In such a situation, as soon as current flows, there may be damage due to this incorrect polarity. Some of the common damage that may occur in this situation is:

1. Damage To The Batteries

If one mistakenly connects the positive terminal of one battery to the negative of another, it will create a huge quantity of electricity which will be relayed between the batteries. This electricity will make the batteries heat up quickly leading to the degradation of water to yield oxygen and hydrogen gases within the battery.

The heat can also cause certain components of the battery to melt and the pressure from the gases can make the battery expand and in extreme cases to even explode.

Where the casing of the battery is cracked, the escaping hydrogen gas can ignite with a possible fire outbreak.(Read Also:How To Test A 12-Volt Battery Charger?)

2. Damage To The Jumper Cables

Jumper cables are not designed to carry a huge quantity of electricity which heats it up to very high temperatures. The high temperature can cause the wires to melt with the possible exposure of people to danger on any direct contact with the cables.

3. Other Likely Damage

Fuses can blow due to the incorrect connection of jumper cables which can cause damage to the vehicle’s main electrical system. It can also lead to the damage of the alternator of the car with the charged battery if its engine is left running.

4. Damage Due To Wrong Polarity

Connecting jumper cables incorrectly will cause the reversal of the polarity of the electrical system on the vehicle with a dead battery for a few seconds This reversal, though for mere seconds, can irreparably affect many sensitive electrical parts in most vehicles such as computers and important sensors.

Can An Alternator Drain A Car Battery?

An alternator is known to convert engine power to electricity, which can be used in charging the car’s battery. Certain defects are known to actually make the alternator misbehave by draining the battery it is supposed to charge which inevitably leads to a series of other problems as follows: (Read Also: How Long Does It Take To Charge Car Battery With Alternator?)

1. Insufficient Alternator Voltage

When the alternator is not producing enough power for whatever reason,  it allows the battery to run down. Any alternator that does not produce up to about 13.8 Volts of power when idling cannot be said to be producing enough power to charge a battery and its replacement is the only option.

2. Bad Diode

When the diode is bad, the alternator may consequently execute a draining action on the battery instead of charging it. Ideally, diodes are known to allow current to flow in only one direction, but a bad diode may keep the charging circuit open even with the engine turned off which may allow the battery to die completely.(Read Also:Can I Use Jumper Cables For Inverter?)

3. Wiring Issues

Damaging the wiring between the alternator and the battery, will not keep the battery charged. It is good to know that a broken ground wire at the back of the alternator, a loose battery wire, or even a faulty or dirty cable can stop the alternator from supplying enough charges to the battery.

What Other Reasons Can Prevent Your Car From Starting?

The first thing that will come to mind when any car refuses to start is either a bad battery or alternator or both. Granted,   this is a true contention, but apart from these regular culprits, there are other reasons why your car may not readily start. We shall give an in-depth analysis of these other reasons.

You should take a very close look at your battery terminals with a view to ensuring whether all is well with them. When the terminals of your battery are either corroded or smeared with grime, they can disallow your car from starting. In this case,  you may have to clean and scrub them.

This can be done with a piece of cloth or rag dabbed in baking soda and water. After the cleaning, make sure that the terminals are open and dried despite careful wiping with a dry towel or cloth. The battery can also fail to start your car if it is old and possibly beyond the point where you can affect any repairs on it.

In such a situation, your best bet is to simply replace it. Period. If none of the above causes are complicit in disallowing your car to start, then you should consider problems possibly in the engine such as with the alternator, a blown starter, or some such causes. (Read Also:Does Battery Voltage Drop When It Discharges?)

However, if the problem ends up being something much more than a mere complaint with the battery or alternator, then you may have to refer your case to a specialist for further attention.

Recommended Products

We have spoken at length about batteries, their maintenance, charging, and proper use. To this end, we should look at some vehicle batteries that boast the qualities and all other features we have discussed. We would also go a little further than that by giving you links via which you can both make inquiries about these products as well as make purchases, where and when necessary. These products are:

  • Optima Batteries 8020 -164 35 RedTop Starting Battery: This battery quite unlike many others has a reserve capacity of one and a half hours which is meant to allow you to look for help in case of emergencies. It is known to stand up to the challenges of bad weather because of its polypropylene casing. The battery is said to be at least fifteen times more resistant to vibration than most of its competitors and is sold under friendly terms as well.

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  • AC Delco ACDB24R Advantage AGM Automotive BCI Group 51 Battery: It is very durable against all agents of harsh weather as well as the vibration of driving on rough and corrugated roads, while its calcium-alloy protects it against corrosion and quick abrasions during handling. It is fully compatible with most vehicles and other gadgets.

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  • Interstate Batteries 12V 35AH Sealed Lead Acid (SLA) AGM Deep Cycle Battery: This product has received the commendation and acceptance of OEM, the authority concerned with the quality and safety of all electrical appliances. The item is also compatible with most vehicle types and is sold subject to conditions that are very friendly and protective of the customers. It can withstand the effects of even very harsh and severe weather conditions.

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How Long Will A Car Battery Stay Charged If Disconnected – Conclusions

Car batteries play indispensable roles in the life of any driver or even all road users and it is for this reason that considerable time has been spent in careful research work to make them progressively better and better.

It is easy to see that charging has been taken to an entirely new level with the multitude of ways to go about it;  ranging from the use of electricity at home, jump-starting, the use of a battery charger, and lots more.

To make matters more interesting, there are various ways you can apply to ensure that your charged battery stays charged by fighting to fend off all factors which will prevent that. Every day the technology of car batteries keeps getting better and better.

For the benefit of self-satisfaction and pleasurable motoring at all times, we should make sure that we diligently go through the user manual. This manual will guide us through most problems we are bound to come across and it is for this reason that it is provided, so, use it.

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