The Ultimate Guide To What Is mAh (Milliamp Hour)

Many people often search for &#;what is mAh&#; especially when understanding how much charge a battery can hold and for how long it will run before depleting. Generally, a mAh (milliampere-hour) is equal to one-thousandth of an ampere-hour. They are also used to rate the battery capacities of appliances and gadgets, such as smartphones, laptops, power tools, and other corded appliances.

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One mAh battery can deliver a continuous current of one milliampere for one hour. For example, if you have a smartphone with mAh. Once fully charged, the battery can hold mA. If the draws around 200mA per hour, it should be able to run for 10 hours. In this article, we will discuss mAh meaning in detail, including its importance and what does mAh mean on battery.

What Is mAh (Milliamp Hour)?

mAh is the power measurement over time. But what does mAh stand for? mAh stands for milliampere-hour. In other words, it is the amount of power a battery can hold or how long it will last before recharging. Let us take a simple example to understand the mAh meaning better.

Think of mAh like your car's gas tank. The amount of gas you can fill in the gas tank represents the tank's capacity. If the gas tank is larger, you can go the extra mile before refilling. Similarly, if a battery capacity (or mAh) is larger, it will last longer between the two consecutive charges.

Understanding what is mAh in batteries will help you choose the best solar power generator for home or outdoor adventures. The simple formula to calculate the mAh of a solar panel is:

mAh = Wh * / V or Milliamp hours = Watt-hour * /Volt

For instance, if a battery has a watt-hour of 200Wh and 5V, it will probably consume

Milliamp hours = 200Wh * / 5V = 40,000 mAh

That said, a battery rated at 40,000 mAh can power a device that withdraws 400 milliamps for 10 hours. Now that you know what is mAh, let us understand the importance of mAh and how it differs from charge capacity in the following sections.

The Importance Of mAh

mAh is the most critical factor you'll need to consider when choosing any battery-powered device. But what is mAh in batteries? In layman's terms, mAh is directly related to battery life.

Checking the mAh units is necessary because it will help you understand how much power the battery can store and how long it can work without recharging. To determine the right mAh requirement, you should check the power consumption of your devices.

For instance, if you intend to use the solar generator battery for larger appliances like refrigerators, you'll have to purchase a solar generator with higher mAh. This will ensure that the solar-powered device can run your devices for hours.

However, it's worth noting that only mAh cannot tell you everything about solar generator performance. You should consider other factors, such as the charge controller, inverter, solar panels, etc., to make an informed purchase decision.

Pro Tip: If you're planning to buy a solar-powered device with a lithium-ion battery, you'll need to understand how much power you wish to withdraw. For instance, you'll likely need a higher mAh battery to make your home off-grid, whereas a small mAh battery would work during RV trips, a few days camping, etc.

mAh Vs. Charge Capacity

mAh (milliamp hours) and charge capacity describe the battery capacity or how much power a battery can hold. Even though they represent the same thing, they are used in slightly different contexts.

mAh typically describes the battery capacity in portable devices such as tablets, laptops, etc. It is the unit that indicates the energy any battery can store. On the other hand, charge capacity defines the battery capacity in solar storage systems and electric vehicles. It measures the energy a battery can receive during a charge cycle. It is generally measured in kWh or Wh.

In a nutshell, a charge capacity measures energy, and mAh defines battery capacity.

Point to remember: Capacity and energy are two different concepts. Ampere-hour measures electric charge and defines battery capacity, whereas watt-hour estimates electric energy.

Let us now discuss the relationship between mAh and charge capacity.

Watt-hour = Milliampere hour * Voltage /

Suppose you have a battery with mAh. That means it can provide a total charge of mAh at a specific voltage. If the voltage at which the charge is exchanged is 3.7V. Thus, in this case, the total energy will be mAh * 3.7V / = 38Wh (approximately).  

What Is mAh Rating Meaning?

mAh rating is the storage capacity of the battery indicated on it. In other words, it represents the fuel the battery can hold to power up the appliance.

Formula: mAh rating is the product of milliampere and hour and can be abbreviated as mAh = mA * H.

Here is an example to understand better. Suppose a battery is rated at 6V, mAh. This indicates that the battery can supply 6 volts at 100mA for 15 hours (100mA*15H = mAh).

The higher the mAh rating, the more the battery storage capacity.

What Does mAh Mean On Batteries?

mAh is commonly used to describe the battery capacity and is the unit of electric charge. Higher mAh batteries are designated in Ah (or ampere-hours), where 1 Ah = mAh. The larger the mAh rating of the battery, the more electrical energy it can store. As a result, only a battery with high mAh can run your device for long hours.

What Does mAh Mean On A Mobile Battery?

The mAh rating on the mobile battery refers to the battery's capacity in terms of mAh (milliampere-hour). Therefore, it is the most suitable parameter to represent the amount of electrical charge stored in the mobile battery.

The formula to calculate the backup time of the smartphone batteries is:

Backup time = mAh rating / current discharged in mA.

Let's calculate how many hours can a mAh battery last:  For instance, if you insert a mAh battery into a device that consumes 200 milliampere current continuously, the operating time or backup time of the appliance will be 10 hours. The device will run for 10 hours before the battery runs out of charge.

What Does mAh Mean On A Rechargeable Battery?

Unlike use-and-throw batteries, rechargeable batteries can be charged again after depletion. They can be recharged thousands of times and can power up high-power-consuming devices. The mAh on rechargeable batteries can be considered the same as simple batteries.

What Does mAh Mean On A Car Battery?

Generally speaking, mAh on your car battery indicates how long you can go without recharging your car. It is a measure of how much electricity the car battery can hold.

Higher mAh ratings of car batteries mean big storage capacities and longer run times. Different car batteries are available; however, the most common ones are lithium-ion and lead-acid batteries.

Lead-acid batteries have a mAh capacity of approximately 135-300 rechargeable cycles. They have an extremely short lifespan and need replacement after every 3-5 years.

On the other hand, lithium-ion batteries have higher mAh and longer lifespans. Their mAh range between 300-400 recharge cycles and last more than 5 years.

mAh to Wh Conversion

Now that we have discussed what does battery mAh mean, it's time to understand how to convert mAh to Wh with one formula.

Both watt hour and milliampere hours are commonly used to describe the battery capacity.

Wh (or Watt hour) is the energy unit equivalent to one watt of power generated or consumed in one hour. It measures the battery's total electrical power to the attached device for an hour.

How To Convert mAh To Wh?

To convert mAh to Wh, you'll need to multiply the charge and voltage. Then you can divide the resultant by to get a watt-hour.

The formula to convert mAh to Wh is:

E (Wh) = Q (mAh) * V /

Where,

E is the energy in watt-hours.

Q is the charge in milliamp hours.

V is the voltage.

Let us calculate the watt-hour of a battery with mAh capacity that works at 120 V.

Energy result in watt-hour = mAh * 120 V / = 120 Wh.

You can also convert Wh to mAh or vice versa using the simple formula: mAh = Wh ÷ V x 1,000, where V represents the battery voltage. If you want to convert mAh to watts, first convert mAh to Wh and then Wh to W.

mAh To Wh Conversion Table

Milliamp-hours

Watt-hours

Amps

100 mAh

12 Wh

120 V

110 mAh

13.2 Wh

120 V

120 mAh

14.4 Wh

120 V

130 mAh

15.6 Wh

120 V

140 mAh

16.8 Wh

120 V

mAh

 240 Wh

120 V

mAh

360 Wh

120 V

mAh

480 Wh

120 V

mAh

600 Wh

120 V

mAh To Ah Conversion 

mAh and Ah are closely related, as they are used for electric charge measurement.

One ampere hour is the electric charge conveyed in one-ampere current in one hour. Amp-hour is designated as amps * hours and is a non-SI metric for electric charge.

Here's how to convert mAh to Ah:

Ah = mAh ÷ .

How To Convert mAh to Ah?

To convert mAh (milliampere-hour) to Ah (amp hour), divide the electric charge by or the conversion ratio.

In simple words, one ampere-hour is equivalent to mAh. Therefore, you can use the simple formula for the conversion.

Ah (amp hour) = milliampere hour ÷

For example, if the mAh of the battery is , the Ah will be mAh ÷ = 2 Ah.

mAh To Ah Conversion Table

Milliamp-hour

Amp-hour

mAh

1 Ah

mAh

1.1 Ah

mAh

1.2 Ah

mAh

1.3 Ah

mAh

1.4 Ah

mAh

1.5 Ah

Jackery Power Station With Best Capacity 

Jackery is the renowned leader in selling portable power stations and solar panels. The rechargeable battery-powered generators have multiple ports, including USB charging ports, an AC outlet, and a DC carport.

The solar power station is built with Battery Management System (BMS) that protects the appliance and product during overcharge, over-voltage, over current, short current, and thermal protection. Below are the top Jackery products with the best battery capacity.

Jackery Explorer 100 Plus Portable Power Station &#; Best For Flights

The Jackery Explorer 100 Plus Portable Power Station is a mini power station that can charge small gadgets and appliances. It weighs only 965 grams and does not emit any noise, making it ideal for business flights. It features multiple output ports to charge up to 3 appliances simultaneously. The LiFePO4 battery can last up to cycles while retaining 80% of its capacity.

Jackery Explorer 300 Plus Portable Power Station &#; Best For Hiking/Photograph

The Jackery Explorer 300 Plus Portable Power Station weighs 8.27 lbs and is an ideal charging solution for hiking and photography adventures. You can charge essential outdoor appliances, such as lights, laptops, camera, smartphone, etc. You can store the portable power station in your backpack and keep charging appliances anywhere you want.

Jackery Explorer 600 Plus Portable Power Station &#; Best For Camping

The Jackery Explorer 600 Plus Portable Power Station is a midsize solar-powered generator that can charge a variety of outdoor camping appliances, from camping lights to coolers. It is a lightweight, powerful, and durable charging solution that can power your adventures for non-stop fun.  It also features a foldable handle to move the power station anywhere you like.  

Product

Capacity

Running Time

Jackery Explorer 100 Plus Portable Power Station

99Wh

(20W) = 4.2H

Laptop (80W) = 1.0H

Camera (9W) = 9.3H

Bluetooth Speaker (10W) = 8.4H

Jackery Explorer 300 Plus Portable Power Station

288Wh

(20W) = 12.2H

Laptop (80W) = 3.0H

Camera (9W) = 27.2H

Bluetooth Speaker (10W) = 24.4H

Lights (10W) = 24.4H

Jackery Explorer 600 Plus Portable Power Station

632Wh

(20W) = 26.8H

Laptop (80W) = 6.7H

Camera (9W) = 59.6H

Bluetooth Speaker (10W) = 53.7H

Lights (10W) = 53.7H

FAQ About mAh For A Battery

Now that we've discussed "what does mAh mean on a battery," here are a few other queries that battery buyers deal with.

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1. mAh Vs. mAh power bank, what are the differences?

The charge stored in the power bank is the product of its mAh (or Ah) rating and terminal voltage. Since the terminal voltage in both cases is the same, i.e., 3.7 volts, the mAh directly defines how much power the power bank can supply.

In the case of mAh and mAh power banks, the latter can store two times more power than the former. That said, mAh power bank stores 3.7 Wh (1 Ah * 3.7), whereas mAh captures 7.4 Wh (2 Ah * 7.4).

In a nutshell, a mAh power bank will hold more charge and power more devices simultaneously than mAh.

2. How to extend the power bank lifespan?

Many power banks have auto-shut qualities that ensure batteries shut down automatically when not in use. However, if the feature is unavailable, the best practice to extend a power bank's lifespan is shutting it down when not required. The next simple step is to charge 80% of the battery and discharge it 20% for at least three months. This will help you to improve the lifespan and battery condition.

3. How to estimate the charge cycles of a power bank?

Understanding "what does mAh mean" is not enough. The charge cycle is another important term representing the efficiency of a power bank. It is the number of complete charges and discharges on a rechargeable battery.

Estimating the charge cycles of a power bank can be calculated by dividing the total available output electric charge by your device's capacity.

Suppose the power bank consists of a 20,000 mAh lithium-ion battery, and the output charge voltage is 5V. So the mWh will be 20,000 mAh * 3.7 V = 74,000 mWh.

Thus, the available output electric charge will be 74,000 mWh / 5V = 14,800 mAh in theory. However, the power bank cannot be 100% efficient. If it's 85% efficient, the actual total output electric charge will be 14,800 mAh * 0.85 = 12,580 mAh.

Now that you have the actual electric charge generated, divide it by your device's capacity to get estimated charge cycles. Here, the charge cycles to power the mAh device will be 12,580 mAh / mAh = 4.33 times.

• How many charges is 10,000mAh?

Every 10,000mAh generally represents roughly 1.5 full charges. A power bank rated at 10,000mAh can last for about 500 charging cycles. A 10,000mAh battery can last up to 10 hours when used heavily.

• Is a 10,000mAh power bank good?

A 10,000mAh power bank is enough to fully charge most gadgets at least once and charge small phones like the iPhone 12 mini three times.

4. What are the benefits of a solar power bank?

Jackery is the leading solar power bank brand that empowers homeowners, campers, and outdoor enthusiasts with clean and renewable electricity. The finest range of portable and versatile generators can keep all your small and large appliances running for hours. Some of the main benefits of choosing Jackery solar generators include the following:

• An eco-friendly energy source that uses the sun's rays to produce electricity.

• The lightweight and portable nature of the power station makes it easy to carry during road trips or camping.

• Unlike gas generators, solar power generators operate in silence and are safe for indoors.

Final Thoughts

"What is mAh?" is the common yet vital question you should ask when purchasing a solar power bank or generator for your power needs. Understating the mAh of your devices reveals the power consumption needs of appliances. Similarly, Ah of solar power systems estimates how long they will last before needing a recharge.

Jackery solar power banks are a reliable source of power that can charge all your home devices. The finest range of Jackery products includes Explorer Pro power station that can charge smartphones, laptops, heaters, cooking equipment, lights, and mini-refrigerators for long hours.

If you intend to choose a power bank with a high mAh battery capacity, Jackery is the best brand for you. Also, don't miss signing up for Jackery's newsletter to get exclusive deals and discounts right in your inbox.

Type of rechargeable battery

"NiMH" redirects here. For other uses, see NIMH

Not to be confused with nickel&#;hydrogen battery

A nickel&#;metal hydride battery (NiMH or Ni&#;MH) is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel-cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although only about half that of lithium-ion batteries.[6]

They are typically used as a substitute for similarly shaped non-rechargeable alkaline batteries, as they feature a slightly lower but generally compatible cell voltage and are less prone to leaking.[7][8]

History

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Disassembled NiMH AA battery:

1. Positive terminal
2. Outer metal casing (also negative terminal)
3. Positive electrode
4. Negative electrode with current collector (metal grid, connected to metal casing)
5. Separator (between electrodes)

Work on NiMH batteries began at the Battelle-Geneva Research Center following the technology's invention in . It was based on sintered Ti2Ni+TiNi+x alloys and NiOOH electrodes. Development was sponsored over nearly two decades by Daimler-Benz and by Volkswagen AG within Deutsche Automobilgesellschaft, now a subsidiary of Daimler AG. The batteries' specific energy reached 50 W·h/kg (180 kJ/kg), specific power up to  W/kg and a life of 500 charge cycles (at 100% depth of discharge). Patent applications were filed in European countries (priority: Switzerland), the United States, and Japan. The patents transferred to Daimler-Benz.[9]

Interest grew in the s with the commercialisation of the nickel-hydrogen battery for satellite applications. Hydride technology promised an alternative, less bulky way to store the hydrogen. Research carried out by Philips Laboratories and France's CNRS developed new high-energy hybrid alloys incorporating rare-earth metals for the negative electrode. However, these suffered from alloy instability in alkaline electrolyte and consequently insufficient cycle life. In , Willems and Buschow demonstrated a successful battery based on this approach (using a mixture of La0.8Nd0.2Ni2.5Co2.4Si0.1), which kept 84% of its charge capacity after charge-discharge cycles. More economically viable alloys using mischmetal instead of lanthanum were soon developed. Modern NiMH cells were based on this design.[10] The first consumer-grade NiMH cells became commercially available in .[11]

In , Stanford Ovshinsky at Ovonic Battery Co., which had been working on MH-NiOOH batteries since mid-,[12] improved the Ti&#;Ni alloy structure and composition and patented its innovations.[13]

In , more than two million hybrid cars worldwide were manufactured with NiMH batteries.[14]

In the European Union due to its Battery Directive, nickel&#;metal hydride batteries replaced Ni&#;Cd batteries for portable consumer use.[15]

About 22% of portable rechargeable batteries sold in Japan in were NiMH.[16] In Switzerland in , the equivalent statistic was approximately 60%.[17] This percentage has fallen over time due to the increase in manufacture of lithium-ion batteries: in , almost half of all portable rechargeable batteries sold in Japan were NiMH.[16]

In BASF produced a modified microstructure that helped make NiMH batteries more durable, in turn allowing changes to the cell design that saved considerable weight, allowing the specific energy to reach 140 watt-hours per kilogram.[18]

Electrochemistry

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The negative electrode reaction occurring in a NiMH cell is

H2O + M + e&#; &#; OH&#; + MH

On the positive electrode, nickel oxyhydroxide, NiO(OH), is formed:

Ni(OH)2 + OH&#; &#; NiO(OH) + H2O + e&#;

The reactions proceed left to right during charge and the opposite during discharge. The metal M in the negative electrode of a NiMH cell is an intermetallic compound. Many different compounds have been developed for this application, but those in current use fall into two classes. The most common is AB5, where A is a rare-earth mixture of lanthanum, cerium, neodymium, praseodymium, and B is nickel, cobalt, manganese, or aluminium. Some cells use higher-capacity negative electrode materials based on AB2 compounds, where A is titanium or vanadium, and B is zirconium or nickel, modified with chromium, cobalt, iron, or manganese.[19]

NiMH cells have an alkaline electrolyte, usually potassium hydroxide. The positive electrode is nickel hydroxide, and the negative electrode is hydrogen in the form of an interstitial metal hydride.[20] Hydrophilic polyolefin nonwovens are used for separation.[21]

Charge

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When fast-charging, it is advisable to charge the NiMH cells with a smart battery charger to avoid overcharging, which can damage cells.[22]

Trickle charging

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The simplest of the safe charging methods is with a fixed low current, with or without a timer. Most manufacturers claim that overcharging is safe at very low currents, below 0.1 C (C/10) (where C is the current equivalent to the capacity of the battery divided by one hour).[23] The Panasonic NiMH charging manual warns that overcharging for long enough can damage a battery and suggests limiting the total charging time to 10&#;20 hours.[22]

Duracell further suggests that a trickle charge at C/300 can be used for batteries that must be kept in a fully charged state.[23] Some chargers do this after the charge cycle, to offset natural self-discharge. A similar approach is suggested by Energizer,[20] which indicates that self-catalysis can recombine gas formed at the electrodes for charge rates up to C/10. This leads to cell heating. The company recommends C/30 or C/40 for indefinite applications where long life is important. This is the approach taken in emergency lighting applications, where the design remains essentially the same as in older NiCd units, except for an increase in the trickle-charging resistor value.[citation needed]

Panasonic's handbook recommends that NiMH batteries on standby be charged by a lower duty cycle approach, where a pulse of a higher current is used whenever the battery's voltage drops below 1.3 V. This can extend battery life and use less energy.[22]

ΔV charging method

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NiMH charge curve

To prevent cell damage, fast chargers must terminate their charge cycle before overcharging occurs. One method is to monitor the change of voltage with time. When the battery is fully charged, the voltage across its terminals drops slightly. The charger can detect this and stop charging. This method is often used with nickel-cadmium cells, which display a large voltage drop at full charge. However, the voltage drop is much less pronounced for NiMH and can be non-existent at low charge rates, which can make the approach unreliable.[23]

Another option is to monitor the change of voltage with respect to time and stop when this becomes zero, but this risks premature cutoffs.[23] With this method, a much higher charging rate can be used than with a trickle charge, up to 1 C. At this charge rate, Panasonic recommends to terminate charging when the voltage drops 5&#;10 mV per cell from the peak voltage.[22] Since this method measures the voltage across the battery, a constant-current (rather than a constant-voltage) charging circuit is used.

ΔT charging method

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The temperature-change method is similar in principle to the ΔV method. Because the charging voltage is nearly constant, constant-current charging delivers energy at a near-constant rate. When the cell is not fully charged, most of this energy is converted to chemical energy. However, when the cell reaches full charge, most of the charging energy is converted to heat. This increases the rate of change of battery temperature, which can be detected by a sensor such as a thermistor. Both Panasonic and Duracell suggest a maximal rate of temperature increase of 1 °C per minute. Using a temperature sensor allows an absolute temperature cutoff, which Duracell suggests at 60 °C.[23] With both the ΔT and the ΔV charging methods, both manufacturers recommend a further period of trickle charging to follow the initial rapid charge.[citation needed]

Safety

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NiMH cell that popped its cap due to failed safety valve

A resettable fuse in series with the cell, particularly of the bimetallic strip type, increases safety. This fuse opens if either the current or the temperature gets too high.[23]

Modern NiMH cells contain catalysts to handle gases produced by over-charging ( 2 H 2 + O 2 &#; catalyst 2 H 2 O {\displaystyle {\ce {2H2{}+O2->[{\text{catalyst}}]2H2O}}} ). However, this only works with overcharging currents of up to 0.1 C (that is, nominal capacity divided by ten hours). This reaction causes batteries to heat, ending the charging process.[23]

A method for very rapid charging called in-cell charge control involves an internal pressure switch in the cell, which disconnects the charging current in the event of overpressure.

One inherent risk with NiMH chemistry is that overcharging causes hydrogen gas to form, potentially rupturing the cell. Therefore, cells have a vent to release the gas in the event of serious overcharging.[24]

NiMH batteries are made of environmentally friendly materials.[25] The batteries contain only mildly toxic substances and are recyclable.[20]

Loss of capacity

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Voltage depression (often mistakenly attributed to the memory effect) from repeated partial discharge can occur, but is reversible with a few full discharge/charge cycles.[26]

Discharge

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A fully charged cell supplies an average 1.25 V/cell during discharge, declining to about 1.0&#;1.1 V/cell (further discharge may cause permanent damage in the case of multi-cell packs, due to polarity reversal of the weakest cell). Under a light load (0.5 amperes), the starting voltage of a freshly charged AA NiMH cell in good condition is about 1.4 volts.[27]

Complete discharge of multi-cell packs can cause reverse polarity in one or more cells, which can permanently damage them. This situation can occur in the common arrangement of four AA cells in series, where one cell completely discharges before the others due to small differences in capacity among the cells. When this happens, the good cells start to drive the discharged cell into reverse polarity (i.e. positive anode and negative cathode). Some cameras, GPS receivers and PDAs detect the safe end-of-discharge voltage of the series cells and perform an auto-shutdown, but devices such as flashlights and some toys do not.

Irreversible damage from polarity reversal is a particular danger, even when a low voltage-threshold cutout is employed, when the cells vary in temperature. This is because capacity significantly declines as the cells are cooled. This results in a lower voltage under load of the colder cells.[28]

Historically, NiMH cells have had a somewhat higher self-discharge rate (equivalent to internal leakage) than NiCd cells. The self-discharge rate varies greatly with temperature, where lower storage temperature leads to slower discharge and longer battery life. The self-discharge is 5&#;20% on the first day and stabilizes around 0.5&#;4% per day at room temperature.[29][30][31][32][33] But at 45 °C (113 °F) it is approximately three times as high.[23]

Low self-discharge

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The low&#;self-discharge nickel&#;metal hydride battery (LSD NiMH) has a significantly lower rate of self-discharge. The innovation was introduced in by Sanyo, branded Eneloop.[34] By using improvements to electrode separator, positive electrode, and other components, manufacturers claim the cells retain 70&#;85% of their capacity when stored for one year at 20 °C (68 °F), compared to about half for normal NiMH batteries. They are otherwise similar to standard NiMH batteries, and can be charged in standard NiMH chargers. These cells are marketed as "hybrid", "ready-to-use" or "pre-charged" rechargeables. Retention of charge depends in large part on the battery's leakage resistance (the higher the better), and on its physical size and charge capacity.

Separators keep the two electrodes apart to slow electrical discharge while allowing the transport of ionic charge carriers that close the circuit during the passage of current.[35] High-quality separators are critical for battery performance.

The self-discharge rate depends upon separator thickness; thicker separators reduce self-discharge, but also reduce capacity as they leave less space for active components, and thin separators lead to higher self-discharge. Some batteries may have overcome this tradeoff by using more precisely manufactured thin separators, and a sulfonated polyolefin separator, an improvement over the hydrophilic polyolefin based on ethylene vinyl alcohol.[36]

Low-self-discharge cells have somewhat lower capacity than otherwise equivalent NiMH cells because of the larger volume of the separator. The highest-capacity low-self-discharge AA cells have  mAh capacity, compared to  mAh for high-capacity AA NiMH cells.[37]

Common methods to improve self-discharge include: use of a sulfonated separator (causing removal of N-containing compounds), use of an acrylic acid grafted PP separator (causing reduction in Al- and Mn-debris formation in separator), removal of Co and Mn in A2B7 MH alloy, (causing reduction in debris formation in separator), increase of the amount of electrolyte (causing reduction in the hydrogen diffusion in electrolyte), removal of Cu-containing components (causing reduction in micro-short), PTFE coating on positive electrode (causing suppression of reaction between NiOOH and H2), CMC solution dipping (causing suppression of oxygen evolution), micro-encapsulation of Cu on MH alloy (causing decrease in H2 released from MH alloy), Ni&#;B alloy coating on MH alloy (causing formation of a protection layer), alkaline treatment of negative electrode (causing reduction of leach-out of Mn and Al), addition of LiOH and NaOH into electrolyte (causing reduction in electrolyte corrosion capabilities), and addition of Al2(SO4)3 into electrolyte (causing reduction in MH alloy corrosion). Most of these improvements have no or negligible effect on cost; some increase cost modestly.[38]

Compared to other battery types

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Alkaline Batteries

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NiMH cells are often used in digital cameras and other high-drain devices, where over the duration of single-charge use they outperform primary (such as alkaline) batteries.

NiMH cells are advantageous for high-current-drain applications compared to alkaline batteries, largely due to their lower internal resistance. Typical alkaline AA-size batteries, which offer approximately 2.6 Ah capacity at low current demand (25 mA), provide only 1.3 Ah capacity with a 500 mA load.[39] Digital cameras with LCDs and flashlights can draw over 1 A, quickly depleting them. NiMH cells can deliver these current levels without similar loss of capacity.[20]

Devices that were designed to operate using primary alkaline chemistry (or zinc-carbon/chloride) cells may not function with NiMH cells. However, most devices compensate for the voltage drop of an alkaline battery as it discharges down to about 1 volt. Low internal resistance allows NiMH cells to deliver a nearly constant voltage until they are almost completely discharged. Thus battery-level indicators designed to read alkaline cells overstate the remaining charge when used with NiMH cells, as the voltage of alkaline cells decreases steadily during most of the discharge cycle.

Lithium-ion batteries can deliver extremely high power and have a higher specific energy than nickel&#;metal hydride batteries,[40] but they were originally significantly more expensive.[41] The cost of lithium batteries fell drastically during the s and many small consumer devices now have non-consumer-replaceable lithium batteries as a result. Lithium batteries produce a higher voltage (3.2&#;3.7 V nominal), and are thus not a drop-in replacement for AA (alkaline or NiMh) batteries without circuitry to reduce voltage. Although a single lithium cell will typically provide ideal power to replace 3 NiMH cells, the form factor means that the device still needs modification.

Lead Batteries

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NiMH batteries can easily be made smaller and lighter than lead-acid batteries and have completely replaced them in small devices. However, lead-acid batteries can deliver huge current at low cost, making lead-acid batteries more suitable for starter motors in combustion vehicles.

As of , nickel&#;metal hydride batteries constituted three percent of the battery market.[25]

Applications

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nickel&#;metal hydride 24 V battery pack made by VARTA, Museum Autovision, Altlussheim, Germany

Consumer electronics

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NiMH batteries have replaced NiCd for many roles, notably small rechargeable batteries. NiMH batteries are commonly available in AA (penlight-size) batteries. These have nominal charge capacities (C) of 1.1&#;2.8 Ah at 1.2 V, measured at the rate that discharges the cell in 5 hours. Useful discharge capacity is a decreasing function of the discharge rate, but up to a rate of around 1×C (full discharge in 1 hour), it does not differ significantly from the nominal capacity.[26] NiMH batteries nominally operate at 1.2 V per cell, somewhat lower than conventional 1.5 V cells, but can operate many devices designed for that voltage.

Electric vehicles

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GM Ovonic NiMH Battery Module

NiMH batteries were frequently used in prior-generation electric and hybrid-electric vehicles; as of they have been superseded almost entirely by lithium-ion batteries in all-electric and plug-in hybrid vehicles, but they remain in use in some hybrid vehicles ( Toyota Highlander, for example).[42] Prior all-electric plug-in vehicles included the General Motors EV1, first-generation Toyota RAV4 EV, Honda EV Plus, Ford Ranger EV and Vectrix scooter. Every first generation hybrid vehicle used NIMH batteries, most notably the Toyota Prius and Honda Insight, as well as later models including the Ford Escape Hybrid, Chevrolet Malibu Hybrid and Honda Civic Hybrid also use them.

Patent issues

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Stanford R. Ovshinsky invented and patented a popular improvement of the NiMH battery and founded Ovonic Battery Company in . General Motors purchased Ovonics' patent in . By the late s, NiMH batteries were being used successfully in many fully electric vehicles, such as the General Motors EV1 and Dodge Caravan EPIC minivan.

This generation of electric cars, although successful, was abruptly pulled off the market.[citation needed]

In October , the patent was sold to Texaco, and a week later Texaco was acquired by Chevron. Chevron's Cobasys subsidiary provides these batteries only to large OEM orders. General Motors shut down production of the EV1, citing lack of battery availability as a chief obstacle. Cobasys control of NiMH batteries created a patent encumbrance for large automotive NiMH batteries.[43][44][45][46][47]

See also

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References

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