A rechargeable battery or storage battery is a group of one or more electrochemical cells. They are known as secondary cells because their electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything from a button cell to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of chemicals are commonly used, including: lead-acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer).
Rechargeable batteries have lower total cost of use and environmental impact than disposable batteries. Some rechargeable battery types are available in the same sizes as disposable types. Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used many times.
Why Rechargeable Batteries
Purchasing rechargeable batteries saves money, protects the environment, and conserves resources. They
can be re-used many times, reducing operating costs and hazardous waste disposal fees. This Fact Sheet
provides information about the most commonly available rechargeable battery, nickel-metal-hydride (NiMH).
NiMH batteries can be used instead of regular non-rechargeable (alkaline) batteries for many applications.
When NOT to Use Rechargeable Batteries
They should NOT be used for emergency equipment
Because they lose up to 1% of their power capacity per day, NiMHs are not good choices for the following:
• Emergency equipment (ie: flashlights, radios, emergency medical devices, etc…)
• Low-power-use devices in difficult-to-access areas (ie: field monitoring devices or ceiling clocks)
At 32°F rechargeables last 20% less time than at room temperature. Capacity drops sharply below freezing.
Types of Rechargeable Batteries
The most popular and readily available “household type” rechargeable batteries today are Nickel-Metal-
Hydride (NiMH). They have advantages over the older rechargeables (Nickel-Cadmium / Ni-Cad) such as:
• Don’t contain cadmium, a toxic heavy metal
• Provide a consistent amount of energy after each charge (no decline over time, ie: no “memory” effect)
• Can be recharged up to 1000 times
• Come in AA, AAA, C, D, and 9-volt sizes
“Rechargeable alkalines” are becoming available from some manufacturers and may be an option if NiMH atteries are not working for your application.
The Charge/Discharge Curve
The measured terminal voltage of any battery will vary as it is charged and discharged
(see Figure ).
The MPV (mid-point voltage) is the nominal voltage of the cell during charge or dis-
charge. The maximum and minimum voltage excursion from the nominal value is an
important design consideration: a “flatter” discharge curve means less voltage variation
that the design must tolerate.
When peak charged, the actual cell voltage will be higher than the MPV. When nearing
the EODV (end of discharge voltage) point, the cell voltage will be less than the MPV.
The EODV is sometimes referred to as the EOL (end of life) voltage by manufacturers.
Basic Battery Characteristics
The electrical characteristics of a battery define how it will perform in the circuit, and the
physical properties have a large impact on the overall size and weight of the product
that it will power.
The key properties and specifications for Ni-Cd, Ni-MH, and Li-Ion will be presented for easy comparison.
Energy Density (By Weight and Volume)
The energy density of a battery is generally expressed in two ways
The gravimetric energy density of a battery is a measure of how much energy a battery
contains in comparison to its weight, and is typically expressed in Watt-hours/kilogram
(W-hr/kg).
The volumetric energy density of a battery is a measure of how much energy a battery
contains in comparison to its volume, and is typically expressed in Watt-hours/liter
the Li-Ion advantage in gravimetric density is clearly
the most striking, almost doubling the Ni-Cd and Ni-MH figures.
This means that products powered by Li-Ion cells can be made much lighter without
sacrificing run time. Alternately, if the battery weight is kept the same, the run time will
double if Li-Ion batteries are used. This fact explains the reason that Li-Ion is quickly
displacing Ni-MH in top-of-the-line cellular phones and laptop computers.
Cell Voltage/Voltage Stability
The voltage provided to power the load is obviously very important: The Ni-Cd and
Ni-MH batteries have a 1.25V nominal cell voltage (their discharge voltages are gener-
ally assumed to be identical).
The Ni-Cd/Ni-MH cell voltage is only about one-third of the nominal 3.6V provided by a
Li-Ion cell which means a designer is required to use three series-
connected Ni-Cd or Ni-MH cells to equal the voltage of a single Li-Ion cell.
However,it shows the biggest advantage of Ni-Cd and Ni-MH batteries:
their discharge curve is extremely flat, closest to an ideal battery.
This important difference between the battery types means that Ni-Cd and Ni-MH cells
are well suited for use with linear regulators, but Li-Ion batteries require switching con-
verters to obtain good energy conversion efficiency in the power supply.
Peak Current
The maximum current that a battery can deliver is directly dependent on the internal
equivalent series resistance (ESR) of the battery.
The current flowing out of the battery must pass through the ESR, which will reduce the
battery terminal voltage by an amount equal to the ESR multiplied times the load current
(V = I X R).
More important, the current flowing through the ESR will cause power dissipation within
the battery that is equal to the ESR multiplied times the current squared (P = I2X R).
This can result in significant heating within the battery at high rates of discharge.
Both Ni-Cd and Ni-MH batteries have extremely low ESR values (well below 0.1W for a
typical “AA” cell), which means that ESR is almost never a limitation for peak discharge
current in these cell types.
The Li-Ion battery will typically have a higher ESR (compared to Ni-Cd or Ni-MH), but
will probably not be a problem in most applications.
Self Discharge
Self-discharge (which occurs in all batteries) determines the “shelf life” of a battery.
it shows typical self-discharge rates for the three chemistries, exact values will
vary with manufacturer.
In general, Li-Ion is the best of the lot, while Ni-Cd and Ni-MH are fairly comparable to
each other. Ni-Cd is typically a little better than Ni-MH, but this may even out as Ni-MH
manufacturing technology matures.
It is important to note that self-discharge is highly dependent on temperature, increasing
as the battery temperature is increased.
Another unpleasant characteristic (I have heard voiced with respect to Ni-MH batteries
used in cellular phones and laptop computers) is that the discharge rate is extremely
non-linear. A battery which loses 30% in a month may lose 15 to 20% in the first few
days (not good if you are taking a couple of spare batteries on a week-long trip, and you
don’t want to carry the charging station).
CELL TYPE NI-MH NI-CD LI-ION
Recharge Time
The amount of time that the typical consumer finds acceptable for battery recharging is
highly variable, and depends on the item being powered. shows the typical
minimum charging times for slow and fast charging rates of the three battery types.
SLOW CHARGING
“Slow” charge is defined as a charging current that can be safely applied to a battery
indefinitely without any kind of monitoring or charge termination method (it is sometimes
referred to as trickle charging). A typical Ni-Cd battery will easily tolerate c/10, and
some fast-charge Ni-Cd cells will accept up to c/3.
Ni-MH cells are not as tolerant of constant charging, as most will not handle a sustained
charging current greater than c/40 (although one manufacturer advertises cells that are
rated for c/10 trickle charge rate).
It is important to note that Li-Ion cells will not tolerate trickle charging at all after they are
fully charged. If current is continuously forced into a fully-charged Li-Ion cell (even a
very minute current) the cell will be damaged. For this reason, Li-Ion cells are charged
using constant-voltage (C-V) chargers, and not constant-current (C-C) chargers.
If a product is designed only for slow (overnight) recharging, a user may have to buy a
second battery pack, and keep it on “standby” charge (increasing the amount of money
he has to spend).
FAST CHARGING
“Fast” charge (usually defined as a 1 hour recharge) requires more complex charging
circuitry (again raising the system cost) but gives the customer faster charging time (a
very attractive selling point).
The typical Ni-Cd or Ni-MH fast charger simply pumps current into the battery, and waits
for the battery to signal when its had enough. Because of the possibility of battery
damage and user safety hazards, fast-charge systems must be designed to accurately
monitor battery parameters like cell temperature and voltage. In addition, most have
back up timers for fail-safe cutoff of the high current charge applied to the battery
Usage and application of these batteries
Rechargeable batteries are used for automobile starters, portable consumer devices, light vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), tools, and uninterruptible power supplies. Emerging applications in hybrid electric vehicles and electric vehicles are driving the technology to reduce cost and weight and increase lifetime.
Normally, new rechargeable batteries have to be charged before use; newer low self-discharge batteries hold their charge for many months, and are supplied charged to about 70% of their rated capacity.
Grid energy storage applications use rechargeable batteries for load leveling, where they store electric energy for use during peak load periods, and for renewable energy uses, such as storing power generated from photovoltaic arrays during the day to be used at night. By charging batteries during periods of low demand and returning energy to the grid during periods of high electrical demand, load-leveling helps eliminate the need for expensive peaking power plants and helps amortize the cost of generators over more hours of operation.
The US National Electrical Manufacturers Association has estimated that U.S. demand for rechargeable batteries is growing twice as fast as demand for nonrechargeables.
Why do batteries become warm when charging?
It is normal for batteries to become warm during the charge cycle. This is caused by the energy the charger is putting into the battery. In general, the shorter the charge time, the warmer the batteries will become.
Information on different typesOf batteries
Nickle Cadmium Batteries (NiCd)
(1)These are the worst type of rechargeable batteries there could possibly be. THERE IS NO REASON THAT PEOPLE SHOULD BE USING THEM ANYMORE. THEY SHOULD BE BANNED. First of all, they are susceptible to the “memory effect” (which I will explain later because no one knows about that either). Second of all, their lifespan when they are treated properly is about a year or two. When abused, they can last six months to a year. You know that the battery is worn out when you have to charge it every day and it only lasts five minutes.
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Another bad thing about these disgusting batteries is that they are terrible for the environment and no one disposes of them properly. They’re heavy and have the least power out of the other types I will mention. These batteries are most commonly found in cheap cordless phones and things like that. It’s a damn shame that there is no such cordless phone with a Lithium Ion battery, (but that’s because they want to make money by selling you more batteries because they go bad often.) They do, however sell them with NiMH batteries (see below), and those are better.
(2) Nickle Metal hydryde Batteries (NiMh)
These are a lot better. They are starting to gain more popularity in cordless phones and are found in some cell phones. There is a 5-10 percent chance that these batteries will be affected by the dreadful memory effect.
NiMH batteries provide the same voltage as NiCd batteries. However, they have at least 30% more battery life than NiCd batteries but take approximately 20% longer to charge. First several times that you charge your Nickel Metal Hydride battery, trickle charge (slow charge) it, this will condition the battery. Unlike Nickel Cadmium, the Nickel Metal Hydride battery can withstand random charging. Never overheat these batteries because that is the worst thing.
(3) Lithium Ion batteries
Excellent!! No memory effect at all. Sony camcorders use these and those batteries are called “InfoLithium” because the camera can determine exactly how many more minutes are left. Smart!!! Anyway besides that you can charge these anytime you want and there shouldn’t be any trouble. Of course all rechargeable batteries wear out over time but these are by far the best ones!! My phone once lasted two weeks before I had to recharge it. See what I mean.
And now… Technical stuff!!! Lithium Ion batteries are at least 30% lighter in weight, and carry at least 30% more capacity than their NiMH or NiCad counterparts. Lithium Ion batteries do require a special type of charger because of their unique charging requirements. While Lithium Ion never has a memory effect, it does prefer to be charged at a rate somewhere between conventional slow chargers and a rapid charge. The battery will accept a rapid charge, but must be slow charged the last 15% of it’s charge cycle. Overheating will damage the battery and could cause a fire.
(4) Lithium Polymer batteries
This the newest battery type being used in cell phones and are rarely used (yet). They have a higher power density than the other types. This allows manufacturers to provide either a thinner or lighter battery, or some combination of both. They are often hard to find. Lithium Polymer batteries do not suffer from the dreaded memory effect and can be recharged anytime. Go to Wikipedia to learn more.
And now… Technical stuff!!! Lithium Ion batteries are at least 30% lighter in weight, and carry at least 30% more capacity than their NiMH or NiCad counterparts. Lithium Ion batteries do require a special type of charger because of their unique charging requirements. While Lithium Ion never has a memory effect, it does prefer to be charged at a rate somewhere between conventional slow chargers and a rapid charge. The battery will accept a rapid charge, but must be slow charged the last 15% of it’s charge cycle. Overheating will damage the battery and could cause a fire.
Alternatives of rechargeable batteries
Several alternatives to rechargeable batteries exist or are under development. For uses such as portable radios, rechargeable batteries may be replaced by clockwork mechanisms which are wound up by hand, driving dynamos, although this system may be used to charge a battery rather than to operate the radio directly. Flashlights may be driven by a dynamo directly. For transportation, uninterruptible power supply systems and laboratories, flywheel energy storage systems store energy in a spinning rotor for conversion to electric power when needed; such systems may be used to provide large pulses of power that would otherwise be objectionable on a common electrical grid. Ultracapacitors are also used; an electric screwdriver which charges in 90 seconds and will drive about half as many screws as a device using a rechargeable battery was introduced in 2007, and similar flashlights have been produced.
Ultracapacitors-capacitors of extremely high value-are being developed for transportation, using a large capacitor to store energy instead of the rechargeable battery banks used in hybrid vehicles. One drawback to capacitors compared with batteries is that the terminal voltage drops rapidly; a capacitor that has 25% of its initial energy left in it will have one-half of its initial voltage. Battery systems tend to have a terminal voltage that does not decline rapidly until nearly exhausted. This characteristic complicates the design of power electronics for use with ultracapacitors. However, there are potential benefits in cycle efficiency, lifetime, and weight compared with rechargeable systems. China started using ultracapacitors on two commercial bus routes in 2006; one of them is route 11 in Shanghai
Loop of a battery
This can be shown by
A digram
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