How to quickly drain a car battery

Discharging a car battery: how to do it correctly

Situations when there is a need to discharge the energy source in a car are rare. This is mainly due to the restoration of the functionality of the product after its severe loss. At first glance, there seems to be nothing complicated here. However, this is not entirely true: the procedure must be controlled, preventing the voltage from falling below a specified level. Once it is reached, the discharge must be stopped or it will stop automatically in accordance with the initially installed program. If the process is not controlled and you do not know the rules for how to discharge a car battery, everything can end sadly: the battery will partially lose capacity, which can no longer be restored. Batteries with calcium electrodes are especially sensitive to complete loss of performance.

Why drain your car battery?

The need for the procedure may arise, for example, for the so-called training charge-discharge. This operation is recommended to be carried out annually (preferably before the onset of cold weather). The result will be an increase in the service life of the current source. Another reason to start discharging a battery is the desire to find out its specific capacity. Initially, the battery is charged to 100%, and then discharged, noting the process time. As a result, you can see the result showing the actual state of the battery in the form of capacity at the moment.

What current should be used to discharge a car battery without damaging it?

The optimal value is 5 A. It is not recommended to discharge the battery with a higher current; this negatively affects the durability of the electrode plates. First you need to determine the voltage at the battery terminals using a device. Then test every 4 hours. As soon as the voltage drops to 11 V, monitor the device every 15 minutes. When a value of 10.5–10.9 V appears, stop the discharge and remove the wires from the battery terminals.

Determination of capacity by discharge

If you discharge a battery with an original (factory) capacity of 60 A*h, and the discharge time at a current of 5 A was 6 hours, then the actual state of the battery can be calculated using the formula Q = 5x6, that is, 30 A*h. Obviously, in this case, half of the capacity is lost.

What can be used as a load?

The simplest option is a 60 W car lamp. There are more complex examples than draining a car battery. If you find a powerful rheostat that can hold 5 or more amperes, that will do. Connect it to the circuit together with the ammeter in series. The voltmeter is connected in parallel to the battery contacts. Now, by moving the rheostat knob, set the required current and at the same time observe the voltage. How long does it take for a car battery to discharge? It all depends on the type of battery and capacity. Usually it is 6–10 hours. Below is an electrical circuit diagram of this discharge method:

Another way is to use a voltmeter. The device is simply connected to the battery, and you watch the voltage drop on its scale or display. The process is lengthy, so when choosing this method, preference should be given to a special powerful repair tester.

And finally, the most reliable method is to use a multifunctional charger (for example, iMAX B6). With its help, you can safely discharge batteries of any type. Everything happens automatically. You only need to set the discharge program at the beginning of the process: current, voltage. The procedure will end automatically: the device will sound a signal. By the way, you can charge the battery with the same charger. Many people ask the question “How to quickly drain a car battery?” Yes, you can connect a more powerful load, the process will go faster, but then the service life of the product will certainly decrease.

Discharging the battery without removing it from the car

Quite a simple method. If there is a voltmeter on the dashboard, no additional devices will be needed. Algorithm of actions:

Turn off the engine.
Use energy consumers: high beam, heated glass, heater.
Monitor the voltage drop using an on-board voltmeter or a separate tester.
When the voltage decreases to 10.9 V, stop the process.

Discharge using improvised means outside the vehicle

If the battery is being discharged outside the car, the best option to obtain the required 5 A current is to use a 60-65 W car lamp. But first you will need to measure the density of the electrolyte, which should be in the range of 1.27–1.29. After checking, connect the lamp parallel to the battery contacts and attach the probes of a multimeter to them, set to voltage measurement mode with an upper limit of 20 V. Monitor the process as described above until the voltage drops to 10.9 V. Note that the load lamp will heat up, so place some non-flammable material under it.

How can you tell if your car battery is completely discharged?

You can determine it by the voltage at the battery contacts. It will be in the range of 10.3–10.9 V. If you have a serviceable battery, then you can verify that it is completely discharged by the density of the electrolyte, which will be less than the standard value of 1.27 g/cubic meter. cm (approximately 1.11–1.13). Once you have realized that the battery is discharged to the required state, you need to charge it as soon as possible: it is undesirable to keep the battery discharged for a long time - this can lead to irreversible chemical processes and, as a result, irreparable loss of capacity.

When should the charging process begin?

This should be done when all the signs described in the previous paragraph are present. How to properly restore the functionality of a specially severely discharged battery? The battery is charged in the normal, normal mode. First check the density of the electrolyte. It will be low (as it should be on a discharged battery): at a voltage of 11.7 V – 1.11–1.13. If the battery has not been removed from the car, then disconnect all power consumers before the process, and it is best to remove both wires from the battery terminals. If you have a budget transformer charger, then set the current in accordance with the capacity of the battery: if, for example, it is 70 A*h, then the value on the ammeter should correspond to 7 A. On the battery being serviced, unscrew the plugs for free gas outlet. Further actions:

If bubbles appear in the battery jars, stop the process for half an hour.
As soon as the battery has cooled, reconnect the charger, but reduce the current by 10 times.
If the solution boils again, take a break again.
After completing the procedure, check the battery voltage (12.6–12.7 V) and electrolyte density (1.27).

What's the result?

As you can see, discharging the battery, although simple, is not without some nuances. Of course, the best option is to use a multifunctional charger, with which you can immediately charge the battery. But if you don’t have such a device at your disposal, and you know how to properly discharge the battery, you should use simple methods: the effect will not be worse, but the process must be constantly monitored.

How to properly discharge a car battery?

02/21/2017 6440 Views 0 Articles,

At first glance, this is an absurd question. But only at first glance. If the battery is no longer as strong as it was immediately after purchase, it can be given a “second wind” by sequentially discharging and then fully charging. This procedure is even desirable; it should be carried out before the cold season.

Let’s say right away: “discharging a battery” does not mean subjecting it to a deep discharge.

That is, turning on all on-board systems with the engine off and waiting for the battery to give up all its energy is a dead end. A calcium battery will not survive such a procedure at all; batteries of other classes will not react very well to it either. It is necessary to discharge to clearly defined electrical parameters. Namely: 10.3 V on the battery as a whole and 1.7 V on each bank. We repeat: the procedure is only suitable for low-antimony batteries; it is better to limit other classes of batteries to a normal charge. But after such a reboot, the batteries of the lead-antimony system can work as in their younger years.

To begin with, how to discharge?

There are several options, but all of them require a multimeter, voltmeter or charger with voltage fixation at the terminals. We connect the equipment to the connected battery and “turn on” the high and low beams. There is no need to connect all the electronics on board - the battery does not like both fast charging and fast discharge. So, we are waiting for the coveted numbers. Afterwards, remove the battery and charge it. If you are near the car without your hand, remove the battery and perform all the manipulations at home. The best discharge option is to connect a 12 V, 60 W light bulb to the battery. These are installed in car headlights. We’ll just get the required 5 A of consumption. At the same time, you can calculate the real capacity of your battery. If you don’t have a light bulb at hand, any 5-7 A consumer will do.

It’s even more convenient if there is a discharge function on the charger. This option is common on more or less variable devices. All that remains is to set the lower voltage limit, after reaching which the charger will stop discharging.

Next is charging.

It needs to start immediately. If it is not possible to immediately charge the battery, do not even start the discharge procedure - you will destroy the battery. In a completely discharged battery, literally after a couple of hours the sulfation process begins - coating the plates with lead sulfate. The deeper the sulfation, the less likely the battery will work at all. So, immediately after the discharge - charging. Preferably with low currents. If you are not going anywhere in the next few days, that’s ideal. Set the charger to a current of 1.5 to 5 A and wait until the container is completely filled. At 1.5 A, charging may take 2-3 days (depending on the battery capacity), but charging with low currents partially desulfates the battery, and therefore restores its capacity.

Up to two such CTC cycles can be performed at a time. But even one may be enough for the battery to recover and serve you faithfully for another couple of years.

How to quickly drain a car battery

Posted on January 4, 2018 by generator-prosto. No comments yet

There are situations when you need to drain your battery. It would seem that it could be simpler. But here it is important to do the discharge correctly. The battery must not be discharged below a certain limit. Typically this threshold is controlled by voltage and when the lower limit is reached, the discharge is stopped manually or automatically. If the discharge is not stopped in time, this can lead to a deep discharge of the battery. This result is undesirable, especially for calcium batteries. After this, the battery may irreversibly lose part of its capacity. Therefore, you need to know how to properly discharge a car battery. This is what our short article will be about.

Why drain your car battery?

It may be necessary to discharge the battery, for example, if you want to perform a training charge-discharge of the battery. Experts recommend carrying out this procedure at least once a year. It is best to do this in the fall as part of preparing your car for winter. This allows you to increase the service life of the battery.

It may be necessary to discharge the battery if you want to measure the actual capacity of your battery. In this case, the battery is fully charged and then discharged with a fixed current. During the process, the discharge time to a certain voltage is measured (10.3 V total or 1.7 V one bank) and the capacity is calculated. This will help you understand how much capacity the battery has lost from its nominal capacity and what condition it is in. Read more about car battery voltage in the article at the link.

Ways to drain your battery

How to discharge the battery without removing it from the car?

This type of battery discharge is the simplest. Natural, you might say.

If you have an accurate voltmeter in the on-board network, then no auxiliary tools are required. If not, then you need a multimeter to monitor the battery voltage. Otherwise, you will simply miss the moment when you need to stop the discharge. This moment is controlled precisely by the voltage value.

As already mentioned, the lower threshold is 10.3 volts at the terminals of the entire battery or 1.7 for one bank. It is difficult to name a specific discharge time, since on-board consumers are used to draw energy from the battery. And they may have different energy consumption. If you are wondering how much a car battery weighs, read the material at the link.

The discharge process itself is incredibly simple:

Turn off the engine;
Turn on the headlights (radio, heating, windows, heater);
Periodically monitor the battery voltage (with a built-in voltmeter or multimeter directly at the terminals);
After the voltage drops to 10.3 volts, the discharge stops. After this, it is best to immediately charge the battery. It should not be kept in a discharged state.

It is worth saying that discharging the battery in a car is only suitable when you need to simply discharge the battery and nothing else. It is not possible to find out the actual capacity of the battery in this way, since this requires discharging the battery with a fixed current value. And how much do the headlights, stove or radio “eat” during operation? To find out, you will need to place an ammeter in the open circuit to measure the current and note the discharge time. Then you can find out the real capacity. When measuring capacity, before discharging the battery, you need to fully charge it (check the degree of charge by the density of the electrolyte). With this approach, it is easier to remove the battery and discharge it separately, as described below. For details on how to check the battery capacity, read the article at the link.

How to discharge the battery outside the car?

If you want to carry out the control training cycle normally, the battery must be removed from the car. Then fully charge using the mains charger. After this, check the density of the electrolyte in each jar with a hydrometer. On average, this value on a fully charged battery should be in the range of 1.27-1.29 g/cm3. Additionally, you can read the material on how to properly charge a car battery with a charger. You might find this article about choosing a charger for a car battery useful.

Then you need to discharge the battery. To do this you need to assemble the following circuit.

Circuit for discharging a car battery

A voltmeter in the circuit is needed to monitor the voltage. Using an ammeter and rheostat, you set the required discharge current. The current is set based on the mode in which you will discharge the battery. In the 10-hour discharge mode, the current is set to 9% of the nominal battery capacity. For 55 Ah batteries common in passenger cars, the discharge current will be about 4.95 A.

Set the current and maintain it until the voltage at the terminals drops to 10.3 volts. To determine the actual battery capacity, multiply the current in amperes by the discharge time in hours. You get the capacity in Ah.

Discharging car battery with light bulb

If you don't have a rheostat, no problem. A suitable resistance can be made from a 12V car light bulb or several. Choose light bulbs of suitable wattage. For the example above, to get a current of 4.95 A, you need a 12 V light bulb with a power of 60 watts. The rest is the same. Discharge the battery to a voltage of 10.3 volts. Just keep in mind that the light bulbs get hot and you need to put something non-flammable under them.

After a complete discharge, the battery must be charged with direct current as quickly as possible. This way you can charge it in the best possible way. We also recommend reading about why your car battery drains quickly.

Battery discharging with multifunction charger

This way to discharge the battery is the safest and most convenient, but you need to have a multifunctional charger like iMAX B6. Using such devices, you can charge and discharge an acid car battery, lithium, or alkaline. This approach is convenient because you do not need to constantly check with a voltmeter for the end of the discharge. The device will automatically stop the process.

In the case of the iMAX B6, you only need to set the battery type, discharge current and the lower battery voltage threshold at which the process should be stopped. Then the device will discharge the battery and signal the end of the operation. At the same time, it will calculate the actual battery capacity in mAh. Next, by changing the program, you can charge the battery. By the way, the actual capacity can be calculated when charging a fully charged battery. We also advise you to read the article, which explains whether you need to charge a new car battery after purchase.

These are the ways to discharge a battery. If you know other methods, we welcome your comments. Vote in the poll below and rate the article!

What are the ways to drain a car battery?

Why drain your car battery?

Ways to drain your battery

How to discharge the battery without removing it from the car?

This type of battery discharge is the simplest. Natural, you might say.

As already mentioned, the lower threshold is 10.3 volts at the terminals of the entire battery or 1.7 ─ one bank. It is difficult to name a specific discharge time, since on-board consumers are used to draw energy from the battery. And they may have different energy consumption. If you are wondering how much a car battery weighs, read the material at the link.

The discharge process itself is incredibly simple:

Turn off the engine;
Turn on the headlights (radio, heating, windows, heater);
Periodically monitor the battery voltage (with a built-in voltmeter or multimeter directly at the terminals);
After the voltage drops to 10.3 volts, the discharge stops. After this, it is best to immediately charge the battery. It should not be kept in a discharged state.

How to discharge the battery outside the car?

If you want to carry out the control training cycle normally, the battery must be removed from the car. Then fully charge using the mains charger. After this, check the density of the electrolyte in each jar with a hydrometer. On average, this value on a fully charged battery should be in the range of 1.27─1.29 g/cm3. Additionally, you can read the material on how to properly charge a car battery with a charger. You might find this article about choosing a charger for a car battery useful.

Then you need to discharge the battery. To do this you need to assemble the following circuit.

Circuit for discharging a car battery

Discharging car battery with light bulb

Battery discharging with multifunction charger

Correctly discharging a car battery

A variety of situations can occur with a car. One of the most unpleasant is an unexpectedly “dead” battery. It would seem that just yesterday everything was fine - I arrived at the garage, locked the car for the night, and in the morning it would no longer start. And the battery is completely “fresh” - it’s a year or two old. The reason for this turn is improper operation.

After all, when the manufacturer guarantees 3 times its uninterrupted operation, he means that the product will be used in accordance with all the rules. Only then will it last a long time, even longer than 3 years. Correct discharge is one of the important aspects of battery operation. However, this procedure must be carried out correctly, following the technological process developed by specialists.

Do I need to discharge the battery?

First you need to understand: do you need to discharge the battery? To do this, you need to understand the processes occurring in the battery.

During operation, some of the sulfuric acid in the battery precipitates salt on the lead plates. If you charge it in time, most of this salt dissolves again in water and the density of the electrolyte is restored. If the discharge caused all the acid to fall out as salt crystals, then it will never dissolve and, accordingly, the battery will no longer work.

In fact, it is in the formation of an insoluble layer of lead sulfate that the process of battery sulfation consists.

By properly discharging and charging the battery, you can “teach” your battery to dissolve salt, so that the battery remains operational and lasts much longer. Such training should be carried out once a year, preferably in the fall, before transferring the battery to winter operation.

The discharge also helps to determine exactly how much battery life is depleted. To do this, it is discharged with a timer and is also charged according to a timer with constant monitoring of the charge level.

How to discharge correctly?

There are several ways to discharge your battery. The first and simplest way is using a voltmeter. It can be built into the side of the car, but then it must be very accurate and have an accurate measurement scale. If there is no such device on board the car, then you can use a repair tester by connecting it directly to the battery.

It is necessary to closely monitor the readings of the device during discharge in order not to miss the lower permissible level - 10.3 Volts. Each battery takes its own time to do this, depending on the brand of the battery, its service life, ambient temperature and several other aspects.
To discharge, you need to turn on some on-board device, for example, headlights, radio or stove.
As soon as the device readings reach 10.3 Volts, you must immediately turn it off.

It is impossible to accurately measure the battery capacity in this way, since it is impossible to know for sure the current consumption of the device, headlights and how much is spent on wire resistance. To obtain accurate data, the battery must be removed from the vehicle and discharged on a special stand.

In this case, the battery becomes completely contaminated, and the density of its electrolyte in each individual bank is checked. On average, the hydrometer should show 1.27-1.29 g/cm³.
After this, the battery is connected to a circuit with an ammeter, voltmeter and a load with a known resistance. The circuit is configured so that the battery is discharged within 10 hours to a lower level of 10.3 volts.
After discharge, you must immediately begin charging the battery. Also not faster or slower than 10 hours.

In a car store you can purchase universal devices for discharging and charging batteries. They are presented in a fairly wide range, you just need to select a device for a specific type of car. After all, the battery sizes of a small car and a truck are strikingly different.

How to charge a dead battery

To properly charge the battery, you need to perform several steps step by step.

Each battery jar must be filled with distilled water.
Turn on the battery for charging, calculating on the charger the current consumption of 0.1 of the battery capacity.
When bubbles appear in the jars as if boiling, the battery is disconnected from charging for 30 minutes.
After the battery has cooled down, turn it on again for charging, but with a charge current of 0.01, that is, 10 times less than the primary rating.
If after some time the liquid in the jars boils again, you need to interrupt the charge for 30-40 minutes.

A full, correct charge may take more than one day, since the battery will constantly have to be disconnected and then connected to the charger, eliminating the boiling of the liquid. In the future, you need to carefully monitor the level of liquid in the jars and, if necessary, add distilled water to it.

You can restore a completely discharged battery simply by changing the electrolyte in it.

Although this procedure is simple, it still requires high-quality preparation; such work must be carried out in a special room and wearing protective glasses and gloves.

First, the battery must be discharged to 9 volts.
Then, every drop of electrolyte is drained from the cans.
Fresh distilled water is poured in and the battery is infused for 1-2 hours.
Now you can plug the battery into the charger. In this case, the charging current should not be higher than 11 volts.
After 1 hour, it is allowed to increase the charge current to 0.1 of the full battery capacity.
Charging continues until the electrolyte in the jars boils. This will be a signal to reduce the charging current on the basis that the procedure will last for 10 hours.

When the battery is charged, it cannot be used, it must be discharged again using the instructions and charged again. And so several times, only after 4-5 charge-discharge cycles, the battery can be installed on the car and used.

Control training cycle

Any auto electrician will tell you that if you apply a control-training cycle or CTC to your battery, the device will be able to last almost 2 times longer than the period that the manufacturer himself has measured for it.

As already reported, the CTC is capable of cleaning the plates from old salt crystals into which sulfuric acid has turned and thereby returning the nominal density to the electrolyte and restoring the area of the working plates to its original state.

If this is not done, the salt gradually covers the lead plate, depriving it of its ability to generate current, and the damaged jar gradually “dies.” A battery with a damaged battery will not hold a charge for long. And for example, the very first frost will completely destroy the battery.

Features of battery discharge

CTC of the battery should be carried out 2 times a year - in spring and autumn. During the period when switching to summer operation of the battery and, accordingly, to winter operation.

You need to discharge the battery only according to the instructions - you cannot simply turn on the headlights and wait until the battery is completely drained - this will simply kill it.
You only need to discharge to the lower permitted limit of 10.3 volts. And the most important thing is to start charging immediately. Also only with special devices and observing the nominal charge current.
In conclusion, we can talk about the reasons for battery discharge and the consequences this leads to. The battery may die due to some kind of current leakage. For example, headlights or a radio tape recorder that are simply forgotten when turned on.
Even the interior light left on overnight can drain the battery to dangerously low levels. And even if everything seems to be turned off, there are hidden current leaks. For example, an alarm or a timer on the same radio.

Another cause of discharge is a broken generator. The task of this device is to constantly recharge the battery, and with a strictly rated current. If the device is faulty, then it will charge the battery incorrectly and thereby destroy it.

Another reason is long parking, especially in winter. Sometimes 2 days off in winter is enough for the battery in a parked car in the yard to go down to zero. To prevent this from happening, it is recommended to disconnect the terminal during long-term parking, that is, break the electrical circuit. Well, or take the battery home, somewhere warm.

Of course, if the battery is relatively new, it can easily withstand 1 or even 2 deep discharges. But if you continue to use it like this, the salt will quickly cover the plates and they will be irrevocably damaged.

In this case, the platinums are replaced with new ones. But the problem is that they don’t produce donor plates now, and inserting old plates from other batteries into your battery is at least not cost-effective. Such a battery with replaced plates does not last long.