What determines the capacity of the battery. Calculation of battery capacity and basic concepts

capacity is charge Q a new battery or a fully charged battery. Charge (amount of electricity) is measured in Coulomb: 1 Coulomb = 1 Ampere × 1 second. Capacitance is usually measured in units of ampere hour or ma hour . Typical battery capacity of AAA size is 1000 mAh, AA - 2000 mAh. A 1000mAh battery can deliver 1000mA for 1 hour or 100mA for 10 hours. Considering the voltage U, then we can estimate the energy stored in the battery E = Q × U

To determine the capacity of the battery, it is fully charged, then discharged with a given current. I, and measure the time T, for which he was discharged. Current product I for a while T and is the battery capacity Q = I × T . The battery capacity is also measured, but after a complete discharge, the battery can be charged again, and the battery can no longer be used. The point is what you measure battery capacity of this type. Incidentally, the capacity alkaline batteries is approximately equal to the capacity of modern NiMh batteries of the same size - AA (2000 mAh), AAA (1000 mAh).

Scheme for capacitance measurement

The proposed circuit discharges the battery through a resistor R to a voltage of almost complete discharge of a NiCd or NiMh element - about 1 volt. The discharge current is I = U / R. (About the selection of the discharge current) To measure the discharge time T clocks are used, operating on a voltage of 1.5-2.5V. To protect the battery from full discharge, a PVN012 solid state relay is used. It cuts off the battery when the voltage drops. U up to the minimum allowable Ue = 1V.

How it works

The battery must be fully charged and connected to the device. The clock must be set to 0 and press the button Start . At this moment, the relay closes contacts 4-5 and 5-6. The battery starts discharging through a resistor R and voltage is applied to the clock. The voltage on the battery and the resistor gradually decreases. When the voltage across the resistor R drops to 1V relay opens contacts. The discharge stops and the clock stops.

As the battery discharges, the control current through the relay contacts 1-2 decreases from about 8 to 2mA. With a control current of 3mA, the resistance of contacts 4-5 and 5-6 is less than 0.04 Ohm. This is small enough not to be taken into account when calculating the current - if you need a discharge current of 1A, take the resistor R = 1.2 Ohm.

After the discharge stops, the voltage on the battery rises to 1.1-1.2V due to the internal resistance of the cell.

Contact losses

When repeating this circuit, take measures to reduce the resistance of the battery contacts and connectors. At a current of 0.5-1A, 0.1V or more can be lost on the contacts, which will degrade the measurement accuracy. The same loss is caused by the steel spring used in some battery holders. The spring and other steel contacts must be shunted with a copper wire. I made one of the AA and AAA battery capacity meter in a case from a simple charger that had good copper contacts.

Additional questions

self-discharge

Please note that the capacity freshly charged batteries are higher, since over time, part of the charge is lost due to self-discharge. To find out the self-discharge value, you need to measure the capacity immediately after charging, and measure it again a week (month) after charging. The self-discharge of NiMh batteries can reach 10% per week or more.

How accurate is capacitance?

The exact amount of electricity can be determined by integrating over time dQ = 1/R × U(t) × dt .

From the experimental discharge graphs, it can be seen that as the discharge progresses, the voltage decreases from about 1.4V to 1.0V. The discharge current U/R also decreases. When used as medium voltage nominal The value of 1.2V results in an accuracy of no worse than 10%. This is true if the battery is used at approximately the same discharge current as when measuring capacity.

Example of discharge charts

If during the measurement there was a current of 0.5A, and when using 5A, then the battery will be discharged several times faster than expected. With a current of use of 0.05A, the capacity will be greater than during the measurement. At a current of 0.005A, the capacity may be less than the measured one due to the self-discharge of the battery during a long period of operation. A significant difference between the measurement current and the operating current introduces an error of more than 10%.

The use of steel contacts in the device instead of copper can increase the error by 10% or more, especially at high discharge current.

Some error in the cutoff voltage value of 1.0V is associated with the dependence of the current-voltage characteristic of a solid-state relay on temperature. In room conditions, this gives an error of 1-2%.

What should be the discharge current?

It is necessary to choose such a current at which this battery is usually used. If the discharge current is too high, then due to internal resistance, the battery voltage will quickly drop below 1 volt, and the measured capacity value will be low. If you choose too low a discharge current, then the measured capacity will turn out to be more than the battery will actually give out when working in your device.

Why two diodes?

Diodes are used to protect the solid state relay in the event of an accidental break in the resistor. R. If you are sure that a break is impossible, or you are measuring the capacity of batteries with a voltage of less than 1.4V ( one AA or AAA element), then the diodes can be removed. In this case, the circuit is placed inside the alarm clock, as I did before. The 5 ohm resistor protects the relay when the Start button is pressed. It can also be removed if you turn on the button in parallel with contacts 4-5, as in the simplified diagram.

How to measure the capacity of a lithium-ion battery?

examples

um	Ue	I	R	r
1.2	1.0	0.2	6.0	0
1.2	1.0	0.5	2.4	0
3.3	3.0	0.5	2.2	4.4
8.4	7.0	0.1	12	72

In this case, a voltage divider is connected to the battery according to the pattern shown in the diagram. Using a voltage divider, you can measure the capacity of a multi-cell battery or a lithium-ion battery.

Required discharge current I at medium voltage um provides the sum of two resistors: R + r = Um / I.

Resistor R calculated so that at the final voltage on the battery Ue, voltage across the resistor R became equal to 1V: R = (Um / I) × (1V / Ue) .

How to check battery capacity by voltage?

Capacitance cannot be determined from voltage. There are typical discharge curves for each type of battery and accumulator. From them, you can estimate the ratio of charge to capacity ( percentage of charge). I am using a charger Ansmann, which for such an estimate measures the voltage at a given discharge current. However, in NiMh batteries, not only the capacity, but also the operating voltage decreases with age. In some cases, Ansmann gave a rating of 30%, while the measurement to full discharge gave 80%.

How to measure battery capacity without this circuit?

Connect a resistor to a charged battery R and a voltmeter. Follow the clock. Over time T voltage U reduced to the minimum allowed. At this point, turn off the resistor. The capacitance is Q = T × U / R

For the safe operation of batteries, you must adhere to the following rules:

• Do not create a short circuit between the battery terminals as the high short circuit current of a charged battery can melt the terminal contacts and cause thermal burns.
• Do not store batteries in a discharged state. In this case, sulfation of the electrodes occurs and the batteries significantly reduce their capacity.
• Connect the battery to the device only with the correct polarity. A charged battery has a significant amount of energy and can, if connected incorrectly, disable the device.
• Do not open the battery case. The gel-like electrolyte contained inside can cause a chemical burn to the skin.
• Dispose of the used battery in accordance with the disposal regulations for products containing heavy metals.

Specifications

Discharge characteristics of rechargeable batteries

The most important indicators of battery quality are: capacity, voltage, dimensions, weight, cost, allowable discharge depth, service life, efficiency, operating temperature range, allowable charge and discharge current. Also, it must be taken into account that the manufacturer gives all the characteristics at a certain temperature - usually 20 or 25 ° C. With deviations from this voltage, the characteristics change, and usually for the worse.

The voltage and capacitance values ​​are usually included in the name of the battery model. For example: - a battery with a voltage of 12 volts and a capacity of 200 ampere * hours, gel, deep discharge. This means that the battery can deliver 12 x 200 = 2400 Wh of energy to the load during a 10-hour discharge with a current of 1/10 of the capacity. With high currents and rapid discharge, the battery capacity decreases. At lower currents, it usually increases. This can be seen on the graph of the discharge characteristics of batteries. Also, you need to look at the discharge characteristics of specific batteries. Sometimes manufacturers write in the name an overestimated battery capacity, which occurs only in ideal conditions - for example, Haze does this (for Haze batteries, the real capacity is 10-20 percent lower than indicated in the battery name).

When discharged with a current of 0.1 C, the operating time is 10 hours and the battery will fully release the accumulated energy to the load. When discharged with a current of 2 C (20 times greater), the operating time will be about 15 minutes (1/4 hour) and the battery will only give half of the accumulated energy to the load. At high discharge currents, this value is even smaller. Often in uninterruptible power supplies, batteries operate in even more difficult modes, in which discharge currents reach 4 C. At the same time, the discharge time is comparable to 5 minutes and the battery delivers less than 40% of energy to the load.

Battery capacity

The amount of energy that can be stored in a battery is called its capacity. It is measured in ampere-hours. One 100Ah battery can supply a load with 1A for 100 hours, or 4A for 25 hours, etc., although the battery capacity decreases as the discharge current increases. Batteries with a capacity of 1 to 2000 Ah are sold on the market.

To increase the life of a lead-acid battery, it is desirable to use only a small part of its capacity before recharging. Each discharge-charge process is called a charge cycle, and it is not necessary to completely discharge the battery. For example, if you discharged the battery by 5 or 10% and then charged it again, this is also counted as 1 cycle. Of course, the number of possible cycles will vary greatly with different depths of discharge (see below). If it is possible to use more than 50% of the energy stored in the battery before it is charged, without a noticeable deterioration in its parameters, such a battery is called a "deep discharge" battery.

Batteries can be damaged if overcharged. The maximum voltage of acid batteries should be 2.5 volts per cell, or 15 volts for a 12 volt battery. Many photovoltaic batteries have a soft load characteristic, so when the voltage increases, the charge current decreases significantly. Therefore, it is always necessary to use a special charge controller for. In the case of wind power plants or micro hydroelectric power plants, such controllers are also required.

Voltage

The voltage on the battery is often the main parameter by which one can judge the condition and degree of charge of the battery. This is especially true for sealed batteries, in which it is not possible to measure the density of the electrolyte.

The voltage during charging, discharging and no current is very different. To determine the degree of charge of the battery, the voltage at its terminals is measured in the absence of both charging and discharging currents for at least 3-4 hours. During this time, the voltage usually has time to stabilize. The value of the voltage during charging or discharging will not say anything about the state or degree of charge of the battery. An approximate dependence of the degree of charge of the battery on the voltage at its terminals in idle mode is shown in the table below. These are typical values ​​for wet starter batteries. For sealed batteries (AGM and GEL) these voltages are usually slightly higher (should ask the manufacturer) - for example, AGM batteries are fully charged if the voltage is 13-13.2V (compare with the voltage of starter batteries with liquid electrolyte 12.5-12.7V ).

Degree of charge

The degree of charge depends on so many factors, and only special chargers with memory and a microprocessor can accurately determine it, which monitor both the charge and discharge of a particular battery for several cycles. This method is the most accurate, but also the most expensive. However, it will be able to save a lot of money on maintenance and battery replacement. The use of special devices that control the operation of batteries according to their degree of charge can greatly increase the service life of lead-acid batteries. A number of solar controllers offered by us have built-in devices for calculating the degree of battery charge and regulate the charge depending on its value.

The following 2 simplified methods can also be used to determine the degree of charge.

1. Battery voltage. This method is the least accurate, but only requires a digital voltmeter capable of measuring tenths and hundredths of a volt. Before measurements, disconnect all consumers and all chargers from the battery and wait at least 2 hours. You can then measure the voltage at the battery terminals. The table below shows the voltages for batteries with liquid electrolyte. For a fully charged new AGM or GEL battery, the voltage is 13-13.2V (compare with wet starter batteries of 12.5-12.7V). As batteries age, this voltage decreases. You can measure the voltage on each cell of the battery to find the bad cell (divide the voltage for 12V by 6 to find the correct voltage for one cell).
2. Second method for determining the degree of charge - by the density of the electrolyte. This method is only suitable for wet batteries.

Also, you need to wait 2 hours before taking measurements. A hydrometer is used for measurement. Be sure to wear rubber gloves and goggles! Keep baking soda and water nearby in case water gets on your skin.

Degree of charge	Battery 12V	Battery 24 V	Electrolyte density
100	12.70	25.40	1.265
95	12.64	25.25	1.257
90	12.58	25.16	1.249
85	12.52	25.04	1.241
80	12.46	24.92	1.233
75	12.40	24.80	1.225
70	12.36	24.72	1.218
65	12.32	24.64	1.211
60	12.28	24.56	1.204
55	12.24	24.48	1.197
50	12.20	24.40	1.190
40	12.12	24.24	1.176
30	12.04	24.08	1.162
20	11.98	23.96	1.148
10	11.94	23.88	1.134

Battery life

It is incorrect to define battery life in years or months. Battery life is determined by the number of charge-discharge cycles and depends greatly on the operating conditions. The deeper the battery is discharged, the more time it is in a discharged state, the fewer possible cycles of operation.

The very concept of “the number of battery charge-discharge cycles” is relative, since it depends heavily on various factors. In addition, the value of the number of operating cycles, for example for one type of battery, is not a universal concept, since it depends on the technology, which varies from manufacturer to manufacturer. Battery life is determined in cycles, so the operating time in years is approximate and calculated for typical conditions. work. Therefore, if, for example, an advertisement states that the battery life is 12 years, this means that the manufacturer has calculated the life for buffer mode with an average number of charge-discharge cycles per month. For example, Haze AGM batteries have a lifespan of 12 years and a maximum number of cycles of 1200 at 20% discharge. There are 100 such cycles per year, about 8 per month.

Another important point is that during operation, the useful capacity of the battery decreases. All characteristics in terms of the number of cycles are usually given not until the battery is completely dead, but until it loses 40% of its nominal capacity. That is, if the manufacturer gives the number of cycles of 600 at 50% discharge, this means that after 600 ideal cycles (i.e. at a temperature of 20C and discharge with a current of the same value, usually 0.1C), the useful battery capacity will be 60% of the initial . With such a loss of capacity, it is already recommended to replace the battery.

Lead-acid batteries designed for use in autonomous power supply systems have a service life of 300 to 3000 cycles, depending on the type and depth of discharge. In RES-based systems, the battery can be discharged much more than in buffer mode. To ensure a long service life, in a typical cycle, the discharge should not exceed 20-30% of the battery capacity, and deep discharge should not exceed 80% of the capacity. It is very important to charge lead-acid batteries immediately after discharging. A long stay (more than 12 hours) in a discharged or not fully charged state leads to irreversible consequences in the batteries and a decrease in their service life.

How can you tell if a battery is nearing the end of its life? Quite simply, the internal resistance of the battery increases, which leads to a faster increase in voltage during charging (and, accordingly, a decrease in the time required for charging), and a faster discharge of the battery. If the charge is made with a current close to the maximum allowable, a dying battery will heat up more when charging than before.

Maximum charge and discharge currents

The charge and discharge currents of any battery are measured relative to its capacity. Typically, for batteries, the maximum charge current should not exceed 0.2-0.3C. Exceeding the charging current will shorten the life of the batteries. We recommend setting the maximum charge current to no more than 0.15-0.2C. See specifications for specific battery models to determine maximum charging and discharging currents.

self-discharge

The phenomenon of self-discharge is characteristic to a greater or lesser extent for all types of batteries and consists in the loss of their capacity after they have been fully charged in the absence of an external current consumer.

For a quantitative assessment of self-discharge, it is convenient to use the value of the capacity lost by them over a certain time, expressed as a percentage of the value obtained immediately after charging. As a rule, a time interval equal to one day and one month is taken as a time interval. So, for example, for serviceable NiCD batteries, a self-discharge of up to 10% is considered acceptable during the first 24 hours after the end of the charge, for NiMH - a little more, and for Li-ION it is negligible and is estimated for a month. Self-discharge in sealed lead-acid batteries is significantly reduced and is 40% per year at 20°C and 15% at 5°C. At higher storage temperatures, self-discharge increases: at 40 ° C, batteries lose 40% of their capacity in 4-5 months.

It should be noted that the self-discharge of batteries is maximum in the first 24 hours after charging, and then significantly decreases. Its deep discharge and subsequent charge increase the self-discharge current.

The self-discharge of batteries is mainly due to the release of oxygen at the positive electrode. This process is further enhanced at elevated temperatures. So, with an increase in ambient temperature by 10 degrees relative to room temperature, a twofold increase in self-discharge is possible.

To some extent, self-discharge depends on the quality of the materials used, the manufacturing process, the type and design of the battery. Capacitance losses can be caused by damage to the separator when agglomerated crystal formations pierce it. A separator is usually called a thin plate separating the positive and negative electrodes. This is usually due to improper maintenance of the battery, its absence, or the use of inappropriate or poor-quality chargers. In a worn-out battery, the electrode plates swell, sticking together, which leads to an increase in the self-discharge current, while the damaged separator cannot be restored by carrying out charge / discharge cycles.

Kargiev Vladimir, "Your Solar House"
© When quoting, a link to this page and to "Your Sunny Home" is required

GLOSSARY

Capacity (C)- the energy that the battery is able to give to the load, expressed in ampere-hours (Ah, mAh). It will be larger under the following conditions: lower discharge current, discharge with shorter interruptions, higher ambient temperature, and lower end voltage.

Rated capacity- nominal value of capacity: the amount of energy that a fully charged battery is capable of delivering when discharged under strictly defined conditions.

self-discharge- loss of capacitance in the absence of an external current consumer.

Battery life- the operating time at which the discharge capacity becomes less than a certain normalized value is usually estimated by the working number of charge-discharge cycles.

A car battery is a device that has a number of characteristics by which it can be selected for a particular vehicle. This article will focus on such a battery parameter as capacity. Below you can find out how to independently determine the capacity of the battery, how this parameter is checked.

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What should a car owner know about battery capacity?

As you know, in total, any car battery has many parameters, including weight, use and storage life, etc. However, one of the most important and key indicators is the battery capacity. For vehicles, this parameter is measured in ampere-hours. WITH Check your vehicle's maintenance manual for the manufacturer's recommended capacity!

Calculation and definition

How to correctly calculate, check and determine the capacity indicator of a car battery? According to this indicator, marked on the battery label, you can determine the level of current strength at which the device is discharged to a minimum voltage of 10.8 V. On average, the duration of traditional discharge cycles should be about 10-20 hours.

For example, if the value of 72 Ah is marked on a car battery, then this indicates that this battery can deliver a current of 3.6 amperes for 20 hours. Accordingly, when the cycle ends, the voltage level at the output should be 10.8 V. However, it must be borne in mind that a car battery is not able to deliver a current of 72 amperes for one hour. When it increases, the discharge time indicator decreases, these parameters are expressed as a power law.

Below is the dependency formula:

Cp = Ik * t, where

• C p - battery capacity level;
• k - the number of Peikert - the scientist who derived the formula;
• t is time.

As for the Peiker coefficient, this is a constant parameter for a certain type of battery. When calculating the characteristics for lead devices, this value is from 1.15 to 1.35. This indicator is determined by the level of the nominal capacity of the battery.

You can also determine by another formula derived to calculate this indicator for an arbitrary parameter of the discharge current:

E =En(I n /I) (p-1) , where

• E n - level of nominal characteristics;
• E - real;
• I n is the level of the discharge current.

Above, we described how to calculate and determine the nominal capacity of the device, but there is still such a moment as the reserve characteristics. If the calculation of the rating is detected by a small current discharge, then the reserve characteristic parameter allows the calculation of the time value. We are talking about the time during which the car battery will be able to function with the generator not running. In this case, a number of 25 amperes is used as the discharge current.

The calculation of the nominal parameter of a car battery can be made by analyzing various design and technological features. It should be noted that this value is strongly influenced by the conditions of use of the battery. Of the main characteristics that determine this indicator, it is necessary to highlight the composition of the electrolyte, the volume of the active mass, as well as the level of thickness of the lead plates. The level of discharge capacity is directly affected by the magnitude of the discharge current, as well as the temperature of the electrolyte (the author of the video is transistor815).

Examination

Many car owners are interested in the question of how to check the capacity measurement of this value on their own. Someone is interested in this just out of curiosity, and someone wants to check the value for compliance with what the manufacturer stated. In principle, it is not so difficult to make a check with your own hands.

Any verification is carried out on the basis of the data given above. For example, for this you can use a meter by conducting a control-training cycle. To properly build a meter, you need a diagram.

The circuit for the meter is shown below. As for the resistance for the meter, it is calculated using the following formula:

• U in this case is the value of the battery voltage;
• I is the value of the discharge current.

To equip the meter, the discharge current should be selected in accordance with the capacity of the battery, as well as the discharge cycle, which can be either 10 or 20 hours. In fact, in most cases, a car lamp with the required power is used for discharge. Using a multimeter, you can measure the exact indicator that passes through the circuit, while it is important to time the time until the voltage drops. Ultimately, the time, which is multiplied by the current, will correspond to the actual battery capacity.

Recovery

So, how is the recovery procedure carried out:

1. To restore the value, a fresh electrolyte is taken, the density of which should be 1.28 k / cm3, in which a special desulfating additive is dissolved. It will take 48 hours for the additive to completely dissolve. For proper recovery, consider all the recommendations described in the instructions.
2. Electrolyte is poured into the car battery, density is measured using a hydrometer, this value should be 1.28 g / cm3.
3. The next stage of recovery will be unscrewing the plugs on the device and connecting it to the charger. In order for the recovery to proceed correctly, you will need to complete several charge and discharge cycles, a minimum current is used for charging, which should be no more than 10% of the maximum. When restoring the battery, it should not heat up or boil. If the voltage rises to 13.8 volts, you need to check the density of the water.
4. Then the electrolyte is adjusted. Distillate is added to the battery banks until the density of the electrolyte is 1.28 g/cm3.
5. Then, for recovery, a discharge is carried out. A load in the form of a light bulb or resistor should be connected to the device, the current in this case should be limited to 1 ampere, if the battery is six-volt, up to 0.5 amperes. You need to wait until the voltage rises to 10.2 volts, while you need to note the time from the moment the load was connected. The resulting discharge characteristic must be multiplied by the time - as a result, you will get the parameter of the required characteristic. If this characteristic is much less than the standard, the discharge-charge procedure must be repeated. This process is repeated until the characteristic is nominal or at least approaches it.
6. At this point, the recovery procedure can be considered complete; additives can still be added to the electrolyte. If you did everything right, then the device will serve you for more than one year.

Battery- this is a device designed to store electrical energy, and the energy in this device is stored in a chemical form.

The principle of operation of the battery is that two metals are in an acid solution, and at the same time they generate electricity. Batteries are characterized by such basic characteristics as:

• capacity
• internal resistance
• self-discharge current
• life time

Battery capacity

Battery capacity is the amount of stored electricity that the battery has. This is one of the most important characteristics of the battery, because the operating time of electrical appliances connected to the battery depends on the capacity.

Battery capacity is measured in milliamp hours (mAh). In this case, the nominal capacity is indicated on the label or directly on the battery. The fact is that the nominal capacity is not always equal to the real one. The actual battery capacity may differ from the nominal in the range from 80 to 110%. This is due to the fact that throughout the life of the battery, its real capacity is gradually changing, as a rule, in the direction of decreasing and, among other things, depends on many additional factors. The operating and maintenance conditions, operating time and method of charging the battery significantly affect the actual capacity.

The difference between nominal and real battery capacity

The electric capacity of the storage battery consists of nominal and real.

Rated capacitance- this is the amount of energy that the battery should theoretically have in a charged state.

This parameter is similar to a container, for example, a glass. Just as 200 ml of water can be poured into a standard faceted glass, only a certain amount of energy can be “pumped” into a battery. But this amount of energy is determined not at the moment of charging, but during the reverse process (when the battery is discharged) by direct current for a measured period of time until the specified threshold voltage is reached.

The capacity is measured in ampere-hours (A / h or mA / h) and is indicated by the letter C. The value of the nominal capacity of the battery is usually encrypted in its designation.

Real capacitance value of a new battery at the time of its commissioning varies from 80 to 110% of the nominal value and depends on the manufacturer, storage conditions and period, as well as on the commissioning technology. The lower limit (80%) is generally considered the minimum acceptable value for a new battery.

Theoretically, a battery, for example, with a nominal capacity of 1000 mAh, can deliver a current of 1000 mA for 1 hour, 100 mA for 10 hours, or 10 mA for 100 hours.

In practice, at a high discharge current, the rated capacity is not reached, and at a low current, it is exceeded. During use, the battery capacity decreases. Decrease rate depends on battery type, service technology, chargers used, operating conditions and length of time.

The internal resistance of a battery determines its ability to deliver high current to the load. This dependence obeys Ohm's law. With a low value of internal resistance, the battery is able to deliver a larger peak current to the load (without a significant decrease in the voltage at its terminals), and hence a greater peak power, while a high resistance value leads to a sharp decrease in the voltage at the battery terminals with a sharp increase in current loads. This leads to the fact that an outwardly good battery cannot fully transfer the energy stored in it to the load.

Typical battery life for different types of batteries and accumulators (when fully charged)

• Nickel-hydride (Ni-MH) batteries - 2 weeks (self-discharge 30% per month).
• Nickel-cadmium (Ni-Cd) batteries - 3 weeks (self-discharge 20% per month).
• Lithium-ion (Li-Ion) batteries - 6 weeks (self-discharge 10% per month).
• Lead acid batteries - 3 months (self-discharge 5% per month).
• Lithium (Li-Metal) batteries - 1 year.

Internal resistance

Internal resistance- also quite an important parameter of the battery. The unit of internal resistance is milliohm (mΩ). Resistance, in turn, depends on the capacity of one cell (bank) of the battery, the number of these cells, battery type, service life and operating conditions. The internal resistance is determined using analyzer devices.

During battery operation, the internal resistance gradually increases. If the battery has a resistance of as much as 500 ohms, then we can conclude that it has a very respectable age or was simply misused.

A large internal resistance leads to an increased consumption of electricity and, as a result, to a shorter operating time of the devices, since, according to Ohm's law, a large resistance significantly increases the consumed current and the simultaneous voltage drop. And with a strong drop in voltage, the connected electrical appliance takes the battery as discharged or simply for one that is not able to work. As a result, the battery cannot deliver all the stored energy, which significantly reduces the operating time of electrical appliances.

Battery self-discharge- This is a spontaneous leakage of electricity from a charged battery for some time. Almost all types of batteries are subject to this phenomenon, regardless of their design and electrochemical type.

Self-discharge is quantified by the amount of energy that a battery loses over a certain period of time, and it is calculated as a percentage of the value of a fully charged battery. The self-discharge value is not constant, so, on the first day after charging, it reaches maximum values, and then gradually decreases.

In this regard, it is customary to measure the value of self-discharge on the first day, and then a month after the charge. The self-discharge is also influenced by the ambient temperature, and the relationship between the self-discharge value and temperature is proportional. It means that as the temperature increases, the self-discharge value also increases.

For example, in some types of batteries, when the temperature rises from 20 to 30 degrees, the self-discharge value doubles. If we talk about its more specific values, then for Ni-Cd type batteries, a value of 10% per day is considered normal, and Ni-MH type batteries have a slightly higher self-discharge value, for Li-Ion and Li-Pol this value is so small that it is evaluated only a month after the charge. As for the monthly value of self-discharge, for the same types of batteries, respectively, we have the following parameters:

• Ni-Cd - 20%
• Ni-MH - 30%
• Li-Ion - 10%

These figures are average, and may vary slightly for each specific battery.

To determine the battery life, the number of cycles between charge and discharge of the battery is used, which it is able to withstand during operation, without significantly changing its main parameters, such as capacity, self-discharge value, and internal resistance.

The time that has elapsed since the battery was manufactured is also taken into account. In the event that the capacity decreases to 60% of the nominal value, the battery is considered to be out of order. The service life is affected by a variety of factors:

• battery type
• charge method
• terms of Use
• correct maintenance

Depending on the electrochemical system used, all batteries are divided into the following types:

• SLA/Pb - classic lead acid
• Ni-Cd - nickel-cadmium
• Ni-MH - nickel metal hydride
• Li-Ion - lithium-ion
• Li-Pol - lithium-polymer, which are a relatively new word in modern technology.

How and why is battery capacity measured?

The charge Q, as the amount of electricity, is measured in coulombs (C), the capacitance of capacitors C is in farads, microfarads (uF), but for some reason it is measured not in farads, but in ampere hours (milliamp hours).

What would that mean? One ampere is a pendant in one second, we know from a physics course that if an electric charge equal to 1 coulomb passes through a conductor in 1 second, then a current of 1 ampere flows through the conductor.

And what then is an ampere-hour? An ampere-hour (Ah) is the battery capacity at which, at a reduced current of 1 ampere, the battery will be discharged in 1 hour to the minimum allowable voltage.

1 ampere hour is 3600 coulombs. Suppose we want to get a battery of capacitors that is equivalent in discharge characteristics, albeit in a short section, to a 12 volt battery with a capacity of 55 ampere-hours. 55 amps for an hour is 55*3600 pendant.

Let's take a voltage change from 13 to 11 volts, then since Q \u003d C (U1-U2), then C \u003d 55 * 3600 / 2 \u003d 99000 F. Almost 100 kilofarads is the equivalent electrical capacity of a car battery if its discharge characteristic were the same as at the condenser.

There is a video on the Internet where six supercapacitors of 3000 F, 2.7 V each, connected in series, replace the car's starter battery. It turns out 500 F at about 16 V.

Let's estimate what current and for how long such an assembly can give. Let the operating range be taken again from 13 to 11 volts. How long can you count on a current of 200 A (with a margin)? I \u003d C (U1-U2) / t, then t \u003d C (U1-U2) / I \u003d 500 * 2/200 \u003d 5 seconds. Enough to start the engine.