What does mah mean? The basic units for measuring battery capacity are Wh and mAh. See what "Ampere-hour" is in other dictionaries

As often happens in our imperfect world, the generally accepted unit for measuring battery capacity has become a unit that cannot accurately reflect the capacity - milliamp-hours (mAh, mAh, mAh). Many manufacturers tried to “instill” in the population the “correct” unit of measurement - watt-hours (Wh, Wh, Wh), but for some reason it has not yet taken root.

Let me explain why watt-hours are the “correct unit” and milliamp-hours (or ampere-hours) are the “wrong” ones. Batteries and battery assemblies come in different nominal voltages, for example 1.2, 3.6, 3.7, 7.4, 11.1, 14.8 V. However, a 7.4 V 2000 mAh battery has twice the capacity of a 3.7 V 2000 mAh, with watt-hours of such confusion it won’t - the first battery has a capacity of 14.8 Wh, the second 7.4 Wh. In this case, to get the watt-hours, I simply multiplied the rated voltage of the battery by the charge in ampere-hours (1Ah=1000mAh).

But that is not all. Let's see how the Li-ion battery from the Cubot S200 smartphone discharges.

During the discharge process, the voltage on the battery changes. For our lithium-ion battery it drops from 4.291 V to 3.0 V.

At the same time, the battery characteristics indicate an average voltage of 3.7 V and a charge in milliamp-hours for this voltage. The real amount of energy that the battery will produce can only be calculated in watt-hours by multiplying the current voltage by the current current at each time and obtaining the final capacity value from the sum of these values, dividing it by the number of such calculations per hour.

The analyzer discharged the battery in 36694 seconds, maintaining a constant discharge current of 301 mA. If we simply multiply 301 by 36694 and divide by 3600 (the number of seconds in an hour) we get 3068 mAh. Let's multiply this value by the nominal battery voltage of 3.7 V and divide by 1000. We get 11.35 Wh.

But what really?

The analyzer measures voltage values ​​10 times per second. By multiplying each voltage value by the discharge current, we obtain the power during each measurement. Let's add up the power values ​​of all 366,913 measurements and divide by the number of measurements per hour (36,000).

With your permission, I will not provide screenshots of 366893 intermediate lines. :)

The resulting value is 11.78 Wh - the real amount of energy that the battery provided. If we divide this value by 3.7V we get a calculated charge of 3184 mAh.

The discrepancy between the actual amount of energy supplied by the battery differs from the calculated one by 3.8%; this is exactly the error that will result if you measure not watt-hours, but milliamp-hours produced by the battery.

In fairness, it must be said that for conventional batteries this discrepancy is usually about one percent.

That is why all devices that measure battery capacity in milliamp-hours give only approximate results, because the voltage changes during the discharge process, and this is not taken into account.

Accurate results can only be given in watt-hours, provided that many measurements are taken during the discharge process.

Why is it so important to pay attention to its capacity when buying a jump starter? The battery life of ROM-powered gadgets depends on it. The capacity of the device is also crucial when starting a car engine - the higher it is, the more times you can try to start the engine.

In ROM descriptions and passports, the capacity may be indicated in mAh and/or Wh. What do these characteristics say?

Capacity value in Wh and mAh - a fundamental difference

The device potential is most accurately described by the absolute constant capacity, measured in Wh. For example, for Carku E-Power Elite it is 44.4 Wh. This means that this device can power a 44.4 W load for one hour at any current and voltage.

If the capacity in Wh is not indicated in the technical specifications of the ROM, it is very simple to calculate it - you need to multiply its value in Ah by the nominal voltage of the battery in volts.
The capacity value in mAh is a relative value that describes the capacity of a device for a specific voltage. That is, for example, for 5 V the battery will have one capacity, and for 19 V - another.

To determine the absolute constant capacity in Wh, you need to know its value in Ah (ampere-hour). 1 Ah = 1000 mAh. To get the capacity in Ah, you need to divide the mAh value by 1000.

What is the rated voltage of Li-Po batteries?

The nominal voltage of a single-cell lithium-polymer battery is 3.7 V. This is exactly the design of the CARKU portable battery chargers. This raises questions for many, because the device has several working connectors with different output voltages - 5 V, 12 V, 19 V? They are obtained from the nominal one as a result of transformations occurring in the electronic filling of the device.

We select CARKU equipment according to technical characteristics

Based on the information provided, you can choose CARKU equipment, focusing on the power of the most commonly used gadgets. For example, if you plan to connect an ASUS N73S laptop to the device, which has a lithium-polymer battery with a capacity of 4,400 mAh, determine its power and compare it with the characteristics of CARKU. For this:
1) convert the capacity value from milliamp-hours to ampere-hours - 4,400 mAh / 1000 = 4.4 Ah;
2) multiply the resulting amp hours by the rated voltage of the lithium polymer battery - 4.4 Ah x 3.7 V = 16.28 Wh.

If you decide to buy the Carku E-Power Elite, which has a capacity of 44.4 Wh, then the laptop connected to a fully charged device will last 44.4 Wh / 16.28 Wh = 2.7 hours. The Carku E-Power-37 model with a capacity of 55.5 Wh will provide 55.5 Wh / 16.28 Wh = 3.4 hours of continuous operation.

For normal operation of any battery, you must always remember "The Three P's Rule":

1. Don't overheat!
2. Do not recharge!
3. Do not overdischarge!

You can use the following formula to calculate the charging time for a NiMH or multi-cell battery:

Charging time (h) = Battery capacity (mAh) / Charger current (mA)

Example:
We have a battery with a capacity of 2000mAh. The charging current in our charger is 500mA. We divide the battery capacity by the charging current and get 2000/500=4. This means that at a current of 500 milliamps, our battery with a capacity of 2000 milliamp hours will charge to full capacity in 4 hours!

And now in more detail about the rules that you need to try to follow for the normal operation of a nickel-metal hydride (Ni-MH) battery:

1. Store Ni-MH batteries with a small amount of charge (30 - 50% of its rated capacity).
2. Nickel-metal hydride batteries are more sensitive to heat than nickel-cadmium (Ni-Cd) batteries, so do not overcharge them. Overloading can negatively affect the battery's current output (the battery's ability to hold and release its accumulated charge). If you have a smart charger with " Delta Peak"(interrupting the battery charge when the voltage peak is reached), then you can charge the batteries with virtually no risk of overcharging and destruction of them.
3. Ni-MH (nickel metal hydride) batteries can (but not necessarily!) be “trained” after purchase. 4-6 charge/discharge cycles for batteries in a high-quality charger allows you to reach the limit of capacity that was lost during the transportation and storage of batteries in questionable conditions after leaving the manufacturing plant. The number of such cycles can be completely different for batteries from different manufacturers. High-quality batteries reach their capacity limit after only 1-2 cycles, while batteries of questionable quality with artificially high capacity cannot reach their capacity limit even after 50-100 charge/discharge cycles.
4. After discharging or charging, try to let the battery cool to room temperature (~20 o C). Charging batteries at temperatures below 5 o C or above 50 o C can significantly affect battery life.
5. If you want to discharge a Ni-MH battery, do not discharge it to less than 0.9V for each cell. When the voltage of nickel batteries drops below 0.9V per cell, most chargers with "minimal intelligence" cannot activate the charge mode. If your charger cannot recognize a deeply discharged cell (discharged less than 0.9V), then you should resort to using a “dumb” charger or connect the battery for a short time to a power source with a current of 100-150mA until the battery voltage reaches 0.9V.
6. If you constantly use the same battery assembly in an electronic device in recharging mode, then sometimes it is worth discharging each battery from the assembly to a voltage of 0.9V and fully charging it in an external charger. This complete cycling procedure should be performed once every 5-10 battery recharging cycles.

Charging table for typical Ni-MH batteries

Element capacity	Standard size	Standard charging mode	Peak charge current	Maximum discharge current
2000 mAh	A.A.	200mA ~ 10 hours	2000 mA	10.0A
2100 mAh	A.A.	200mA ~ 10-11 hours	2000 mA	15.0A
2500 mAh	A.A.	250mA ~ 10-11 hours	2500 mA	20.0A
2750 mAh	A.A.	250mA ~ 10-12 hours	2000 mA	10.0A
800 mAh	AAA	100mA ~ 8-9 hours	800 mA	5.0A
1000 mAh	AAA	100mA ~ 10-12 hours	1000 mA	5.0A
160 mAh	1/3 AAA	16mA ~ 14-16 hours	160 mA	480 mA
400 mAh	2/3 AAA	50mA ~ 7-8 hours	400 mA	1200 mA
250 mAh	1/3AA	25mA ~ 14-16 hours	250 mA	750 mA
700 mAh	2/3 AA	100mA ~ 7-8 hours	500 mA	1.0A
850 mAh	FLAT	100mA ~ 10-11 hours	500 mA	3.0A
1100 mAh	2/3 A	100mA ~ 12-13 hours	500 mA	3.0A
1200 mAh	2/3 A	100mA ~ 13-14 hours	500 mA	3.0A
1300 mAh	2/3 A	100mA ~ 13-14 hours	500 mA	3.0A
1500 mAh	2/3 A	100mA ~ 16-17 hours	1.0A	30.0 A
2150 mAh	4/5 A	150mA ~ 14-16 hours	1.5A	10.0 A
2700 mAh	A	100mA ~ 26-27 hours	1.5A	10.0 A
4200 mAh	Sub C	420mA ~ 11-13 hours	3.0A	35.0 A
4500 mAh	Sub C	450mA ~ 11-13 hours	3.0A	35.0 A
4000 mAh	4/3 A	500mA ~ 9-10 hours	2.0A	10.0 A
5000 mAh	C	500mA ~ 11-12 hours	3.0A	20.0 A
10000 mAh	D	600mA ~ 14-16 hours	3.0A	20.0 A

The data in the table is valid for completely discharged batteries

Battery Capacity Units

When choosing a portable battery charger (ROM), many people ask questions: “What do the mAh and Wh characteristics mean?”, “And why are they needed?”

We answer. Both values: mAh (milliamp-hour) and Wh (watt-hour) characterize the capacity of the charger. But it is most correct to focus on capacity, measured in watt-hours. And that's why.

Wh is an absolute constant capacity that most accurately describes the potential of a device.

And the capacity indicated in mAh is a relative value that describes the capacity of the device in relation only to a specific selected voltage. That is, for one voltage there is one capacitance, and for another voltage there is another capacitance. Often you can also see the designation “Ah” (ampere-hour). 1 Ah = 1000 mAh. Thus, to get the Ah value, you need to divide the mAh value by 1000. Conversely, to get mAh, you need to multiply the Ah value by 1000.

For example, the CARKU E-Power-3 battery charger has a capacity of 29.6 Wh or 8000 mAh (8 Ah).

At the same time, 8000 mAh is the nominal capacity, and it is indicated relative to the nominal voltage of the batteries built into the body of the starter-charger. All lithium polymer (LiPo) and lithium ferrum phosphate (LiFePO4) batteries used in starter chargers have a nominal voltage of 3.7 V. Many will ask: “How so? If the nominal voltage = 3.7 V, then why are the ROM outputs marked with values ​​of 5V, 12V and 19V?” The answer is simple: the voltage increase for one or another ROM output occurs due to the electronic filling of the device.

Thus, for a nominal voltage of 3.7V, the CARKU E-Power-3 ROM has a nominal capacity of 8000 mAh. From this value of nominal relative capacity, expressed in mAh, it is easy to obtain the value of absolute capacity, expressed in Wh:

1) first, convert the capacity value expressed in milliamp-hours to ampere-hours

8 Ah x 3.7 V = 29.6 Wh

Thanks to this ratio, it is easy to calculate the actual capacity in mAh of the CARKU ROM and any other battery at a specific operating voltage of a specific electrical consumer.

Let's make calculations using the example of the CARKU E-Power-3 ROM. This model has 2 outputs:

1) USB output for charging mobile phones, tablets, etc. with an operating voltage of 5 V. To calculate the actual capacity for this operating mode, it is necessary to divide the absolute capacity of 29.6 Wh by the voltage of 5 V, and then we get 5.92 Ah:

29.6 Wh / 5 V = 5.92 Ah (or 5920 mAh).

2) Output for starting a motor with an operating voltage of 12 V. Here the same formula is used to calculate the actual capacity:

29.6 Wh / 12 V = 2.467 Ah (or 2467 mAh).

As we can see from the calculations, the most obvious and correct value characterizing the capacity of the ROM is precisely Wh. And based on it, it is easy to calculate the capacity in mAh for a particular voltage and, therefore, approximately estimate the potential of the ROM for a specific electrical consumer.

The capacity values ​​in mAh for the CARKU E-Power-3 ROM, when correctly calculated for 5V and 12V, are not as impressive as for a nominal voltage of 3.7V, but this does not detract from the high consumer performance of this little one. The compact and lightweight E-Power-3 allows, for example, to fully charge an iPhone4 3 times or a classic Nokia 106 6 times, as well as confidently start 4-liter gasoline engines in summer and 1.6-liter gasoline engines in winter, which is confirmed by real tests and numerous videos in Youtube.

Some into the forest, some for firewood

In ROM descriptions and passports, first of all, it is necessary to indicate the capacity in Wh. Additionally, you can indicate the nominal capacity of the ROM in mAh, paying tribute to the historically popular dimension, easily recognized by the mass consumer and widely used for power banks (external batteries), batteries for mobile phones, tablets, etc.

All CARKU ROMs have an absolute capacity in Wh and a nominal relative capacity in mAh. Some manufacturers incorrectly indicate the ROM capacity only in mAh, reflecting a secondary capacity characteristic and completely forgetting about the most important one.

There are also situations where some sites indicate inflated specifications in mAh. For example, the absolute capacity of the CARKU E-Power-Elite ROM is 44.4 Wh, which means its nominal capacity is 12000 mAh (44.4 Wh / 3.7 V = 12 Ah). Therefore, there cannot be a CARKU E-Power-Elite ROM with an absolute capacity of 44.4 Wh and at the same time with a nominal capacity of 14000 mAh or 15000 mAh, as some sales companies indicate.

It is also worth keeping in mind that the vast majority of portable starter-chargers currently presented on the Russian market have an actual capacity much less than the declared one. For example, 5000 mAh instead of 8000 mAh, 8000 mAh instead of 14000 mAh, etc. The difference between the declared and actual capacity sometimes reaches 2 or more times. This is a very common situation, because it is very difficult for the consumer to check the actual capacity, much less measure it. In turn, the actual capacity of the CARKU ROM fully corresponds to the declared one. This is confirmed, for example, by an independent review of the Russian ROM market and, in which the CARKU ROM demonstrates a greater number of launches than analogues with a larger capacity.

Why is it so important to pay attention to ROM capacity? Because the duration of autonomous operation of electrical consumers powered from the ROM directly depends on it. The capacity of the ROM is especially important in the winter when starting a vehicle engine, since the larger the capacity, the more attempts there will be to start the engine and their duration, and, consequently, the likelihood of a successful start. In addition, the battery is the main element of the ROM, so the cost of the ROM directly depends on its capacity. So keep this in mind when choosing a ROM for yourself.

Hello, dear friends! When choosing a portable battery, you may encounter a large number of negative reviews regarding the discrepancy between their declared capacity and the number of charged gadgets. It would seem that having bought a 13,000 mAh charger, we should charge our smartphone with a 2300 mAh battery about 5.5 times! But it's not that simple.

A little background

As a lover of gadgets and modern technologies, I have a smartphone and other good things. And along a certain path I encountered one, in my opinion, serious problem with advanced devices - they have a relatively short battery life. Yes, I won’t argue, there are telephone-making “monsters” that have batteries of 4000 mAh or more. But, often, such devices are extremely rare and have other disadvantages. In any case, even if your gadget can last until the evening (and my Nexus 5 with 2300 mAh is not on this list), sooner or later the question of buying a portable battery arises.

Like many geeks, I have been itching to buy this type of device for a long time. I was considering the options of buying a box for 18650 batteries, as well as a ready-made device (which most likely contains the same 18650 batteries, just like laptop batteries). As a result, the need arose to have a charged phone at work in the absence of an outlet, and a portable battery DF TRIO-02 was purchased.

To be honest, I didn’t have much time to choose and read reviews. I just quickly combed through one well-known online store (the one that is part of a group of companies along with a bank and a jewelry store) and selected it according to the following criteria:

• required capacity
• price quality
• appearance (yes, yes, you need to strive not only for ergonomics, but also enjoy aesthetically)

Briefly about this very device

Pros:

1. good capacity
2. two outputs of 5V, 1A; one output 5V, 2.1 A
3. microUSB battery charging input

Minuses:

1. Stainless glossy body

Arithmetic for calculating capacity

For ease of calculation, we introduce the following assumptions:

1. We take the efficiency of the voltage converter as 100%
2. we accept all indicated capacities as real values
3. We assume constant values ​​of current and voltage during charging
4. The phone charges from ideal 0% to 100% (without taking into account the residual charge provided by manufacturers, etc.)

To eliminate the inaccuracy, let's take a look at Wikipedia:

The maximum possible useful charge of a battery is called the charging capacity, or simply capacity. Battery capacity is the charge given off by a fully charged battery when discharged to the lowest permissible voltage. In the SI system, the capacity of batteries is measured in coulombs; in practice, a non-systemic unit is often used - ampere-hour. 1 Ah = 3600 C. The battery capacity is indicated by the manufacturer. Not to be confused with the electrical capacitance of a capacitor.

Nowadays, batteries are increasingly indicated with energy capacity - the energy given off by a fully charged battery when discharged to the lowest permissible voltage. In the SI system it is measured in joules; in practice, a non-systemic unit is used - watt-hour. 1 Wh = 3600 J.

On the packaging we have a proud inscription: “13000 mAh”. This is our charging capacity.
Looking carefully at the sticker on the back side we see the following.

Voltage: 3.7 V.
Charging capacity: 13000 mAh.
Energy capacity: 48.1 Wh.

It turns out that many Manufacturers indicate the stored charge in mAh (mAh), but the operating voltage of the device is also important. To the fullest extent, “capacity” characterizes stored energy.

People often confuse the concepts stored charge And stored energy calling it "capacity". If great accuracy is not needed, then we can assume that the stored energy (in Wh) is approximately equal to the product of the stored charge (in Ah) and the average voltage (in Volts).

1 Wh = 1 V 1 Ah.

Now, having understood the concepts, let's move on to our example: 48.1 Wh of battery is 13 Ah (13000 mAh) multiplied by 3.7 V. So far everything fits. But, our device is charged from an output of 5 V. Therefore, the charge that our device is capable of delivering is found as a quotient of the stored energy and the output voltage.
48.1 Wh / 5 V = 9.62 Ah (9620 mAh).

Analyzing

Now you can easily calculate “how many times can I charge my device.” So, the same Nexus 5 can be charged:
9620 mAh/ 2300 mAh = 4.18
Or, in other words, a little more than 4 times. What's against 5.5

Drawing conclusions

The calculated battery capacity of 9620 mAh was 26% less than the 13000 mAh we see on the box. And 26% less than what a user inexperienced in calculations would expect. Although, in fact, the manufacturer did not deceive us at all. It's just a marketing ploy.

Useful articles and sources.