I keep seeing this problem pop up time and time again.
It's time it got its own thread.
It's going to be a rip-off of wikipedia, so I'll link the articles where you can get more info.
Batteries, specifically, rechargeable batteries: how do they work and how to take care of them?
There are several types of rechargeable batteries available. Let's go through them in blocks:
1 - Lead-acid batteries: Usually used in cars, are big and heavy and store quite a little amount of energy for their size and weight, but they can discharge quite rapidly supplying a nice current for a short while.
Electricity is stored as chemical energy. Fully, charged, this is what a cell of this battery looks like:
![[Image: 220px-Recharged.gif]](https://images.weserv.nl/?url=upload.wikimedia.org%2Fwikipedia%2Fen%2Fthumb%2F2%2F25%2FRecharged.gif%2F220px-Recharged.gif)
The cathode (positive side [+]) is on the left, with PbO2 (lead oxide)). On the right is the Anode (negative side [-]) with Pb (lead). In the middle is a liquid acid H2SO4 (Sulfuric Acid).
During discharge, H+ produced at the anode and from the electrolyte solution moves to the cathode where it is consumed, while HSO4− is consumed at both plates. The reverse occurs during charge. This motion can be by diffusion through the medium or by flow of a liquid electrolyte medium.
The acid is diluted into water and the result looks like this:
![[Image: 220px-Discharged.gif]](https://images.weserv.nl/?url=upload.wikimedia.org%2Fwikipedia%2Fen%2Fthumb%2F9%2F99%2FDischarged.gif%2F220px-Discharged.gif)
Lead sulfate on both sides, so nothing to do.
Each cell provides about 2.0V, so your typical 12V car battery contains 6 cells.
Lead-acid batteries designed for starting automotive engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling. Starting batteries kept on continuous float charge will have corrosion in the electrodes which will result in premature failure. Starting batteries should be kept open circuit but charged regularly (at least once every two weeks) to prevent sulfation.
Their Self-discharge rate spans from 3 to 20% per month, so take care when you leave your car unused for a long time.
Finally, they are designed to last for 500 to 800 cycles. A cycle is a discharge (lower than 50%) and recharge (to 100%). If you use the car daily, that's about 350 times per year, but the battery will last for some 3 to 5 years, because you will not discharge it more than 50% on all start-ups.
2 - Nickel Cadmium batteries: Old time rechargeable batteries. Seldom used nowadays, but very common in the heydays of the Walkman.
Ni–Cd cells have a nominal cell potential of 1.2 volts (V). This is lower than the 1.5 V of alkaline and zinc–carbon primary cells, and consequently they are not appropriate as a replacement in all applications. However, the 1.5 V of a primary alkaline cell refers to its initial, rather than average, voltage. Unlike alkaline and zinc–carbon primary cells, a Ni–Cd cell's terminal voltage only changes a little as it discharges. Because many electronic devices are designed to work with primary cells that may discharge to as low as 0.90 to 1.0 V per cell, the relatively steady 1.2 V of a Ni–Cd cell is enough to allow operation. Some would consider the near-constant voltage a drawback as it makes it difficult to detect when the battery charge is low.
These batteries are more difficult to damage than other batteries, tolerating deep discharge for long periods. In fact, Ni–Cd batteries in long-term storage are typically stored fully discharged. This is in contrast, for example, to lithium ion batteries, which are less stable and will be permanently damaged if discharged below a minimum voltage.
Nickel–metal hydride (NiMH) batteries are the newest, and most similar, competitor to Ni–Cd batteries. Compared to Ni–Cd batteries, NiMH batteries have a higher capacity and are less toxic, and are now more cost effective. However, a Ni–Cd battery has a lower self-discharge rate (for example, 20% per month for a Ni–Cd battery, versus 30% per month for a traditional NiMH under identical conditions), although low self-discharge ("LSD") NiMH batteries are now available, which have substantially lower self-discharge than either Ni–Cd or traditional NiMH batteries. This results in a preference for Ni–Cd over non-LSD NiMH batteries in applications where the current draw on the battery is lower than the battery's own self-discharge rate (for example, television remote controls). In both types of cell, the self-discharge rate is highest for a full charge state and drops off somewhat for lower charge states. Finally, a similarly sized Ni–Cd battery has a slightly lower internal resistance, and thus can achieve a higher maximum discharge rate (which can be important for applications such as power tools).
Ni–Cd batteries may suffer from a "memory effect" if they are discharged and recharged to the same state of charge hundreds of times. The apparent symptom is that the battery "remembers" the point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged. The capacity of the battery is not actually reduced substantially. Some electronics designed to be powered by Ni–Cd batteries are able to withstand this reduced voltage long enough for the voltage to return to normal. However, if the device is unable to operate through this period of decreased voltage, it will be unable to get enough energy out of the battery, and for all practical purposes, the battery appears "dead" earlier than normal.
Ni–Cd batteries contain between 6% (for industrial batteries) and 18% (for consumer batteries) cadmium, which is a toxic heavy metal and therefore requires special care during battery disposal.
Their self-discharge rate is about 10% per month.
They can withstand about 2,000 cycles.
Each cell provides 1.2 V.
3 - Nickel Metal Hydride batteries: Newer rechargeable batteries used wherever a standard AA or AAA battery can be used.
The "metal" M in the negative electrode of a NiMH cell is actually 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, and/or aluminium. Very few cells use higher-capacity negative electrode materials based on AB2 compounds, where A is titanium and/or vanadium and B is zirconium or nickel, modified with chromium, cobalt, iron, and/or manganese, due to the reduced life performances.[11] Any of these compounds serve the same role, reversibly forming a mixture of metal hydride compounds.
The charging voltage is in the range of 1.4–1.6 V/cell. In general, a constant-voltage charging method cannot be used for automatic charging. When fast-charging, it is advisable to charge the NiMH cells with a smart battery charger to avoid overcharging, which can damage cells and even be dangerous.[13] A NiCd charger should not be used as a substitute for an automatic NiMH charger.
A fully charged cell supplies an average 1.25 V/cell during discharge, down 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). Under a light load (0.5 ampere), the starting voltage of a freshly charged AA NiMH cell in good condition is about 1.4 volts.
A complete discharge of a battery can result in one or more cells going into polarity reversal, which can cause permanent damage to those cells. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the good cells will start to drive the discharged cell in reverse, which can cause permanent damage to that cell.
NiMH cells historically 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 rate 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. So charge them and use them. Don't charge them and store them!
Improper disposal of NiMH batteries poses less environmental hazard than that of NiCd because of the absence of toxic cadmium. However, mining and processing the various alternate metals that form the negative electrode may pose other types of environmental impact, depending on the metal, mining method, and environmental practices of the mine.
Most industrial nickel is recycled, due to the relatively easy retrieval of the magnetic element from scrap using electromagnets, and due to its high value.
4 - Lithium-ion batteries: They power your phone, your laptop, your tablet... and some airplanes.
With a voltage of 3.7V per cell it is not suitable as a replacement for standard AA or AAA (1.5V) batteries.
They are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, no memory effect, and only a slow loss of charge when not in use.
The participants in the electrochemical reactions in a lithium-ion battery are the negative and positive electrodes with the electrolyte providing a conductive medium for Lithium-ions to move between the electrodes.
Both electrodes allow lithium ions to move in and out of their interiors. During insertion (or intercalation) ions move into the electrode. During the reverse process, extraction (or deintercalation), ions move back out. When a lithium-ion based cell is discharging, the positive Lithium ion moves from the negative electrode (usually graphite) and enters the positive electrode (lithium containing compound). When the cell is charging, the reverse occurs.
Batteries gradually self-discharge even if not connected and delivering current. Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month. The rate increases with temperature and state of charge. A 2004 study found that for most cycling conditions self-discharge was primarily time-dependent; however, after several months of stand on open circuit or float charge, state-of-charge dependent losses became significant. The self-discharge rate did not increase monotonically with state-of-charge, but dropped somewhat at intermediate states of charge. Self-discharge rates may increase as batteries age.
Rechargeable battery life is often stated in number of charge cycles, but depth of discharge is usually not explicitly stated. Apple Inc. clarify that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle.
Batteries may last longer if not stored fully discharged. As the battery self-discharges over time, its voltage gradually reduces. When depleted below the low-voltage threshold of the protection circuit (2.4 to 2.9 V/cell, depending on chemistry) it will be disabled and cannot be further discharged until recharged. This because as the discharge progresses, the metallic contents of the cell are plated onto its internal structure creating an unwanted discharge path. It is recommended to store batteries at 40% charge level.
Since Li-ion batteries contain no toxic metals (unlike other types of batteries which may contain lead or cadmium) they are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, but mining generally remains cheaper than recycling. At present, not much is invested into recycling Li-ion batteries due to costs, complexities and low yield.
The standard recommendation is to keep them charged, as close to 100% as possible. The circuitry will prevent recharge until its natural discharge rate reaches 95%, thus preventing the use of excessive recharge cycles, and keeping the battery always ready to operate when needed.
5 - Others... there are other rechargeable battery technologies, but they are less common and so beyond the scope of this thread.
It's time it got its own thread.
It's going to be a rip-off of wikipedia, so I'll link the articles where you can get more info.
Batteries, specifically, rechargeable batteries: how do they work and how to take care of them?
There are several types of rechargeable batteries available. Let's go through them in blocks:
1 - Lead-acid batteries: Usually used in cars, are big and heavy and store quite a little amount of energy for their size and weight, but they can discharge quite rapidly supplying a nice current for a short while.
Electricity is stored as chemical energy. Fully, charged, this is what a cell of this battery looks like:
The cathode (positive side [+]) is on the left, with PbO2 (lead oxide)). On the right is the Anode (negative side [-]) with Pb (lead). In the middle is a liquid acid H2SO4 (Sulfuric Acid).
During discharge, H+ produced at the anode and from the electrolyte solution moves to the cathode where it is consumed, while HSO4− is consumed at both plates. The reverse occurs during charge. This motion can be by diffusion through the medium or by flow of a liquid electrolyte medium.
The acid is diluted into water and the result looks like this:
Lead sulfate on both sides, so nothing to do.
Each cell provides about 2.0V, so your typical 12V car battery contains 6 cells.
Lead-acid batteries designed for starting automotive engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling. Starting batteries kept on continuous float charge will have corrosion in the electrodes which will result in premature failure. Starting batteries should be kept open circuit but charged regularly (at least once every two weeks) to prevent sulfation.
Their Self-discharge rate spans from 3 to 20% per month, so take care when you leave your car unused for a long time.
Finally, they are designed to last for 500 to 800 cycles. A cycle is a discharge (lower than 50%) and recharge (to 100%). If you use the car daily, that's about 350 times per year, but the battery will last for some 3 to 5 years, because you will not discharge it more than 50% on all start-ups.
2 - Nickel Cadmium batteries: Old time rechargeable batteries. Seldom used nowadays, but very common in the heydays of the Walkman.
Ni–Cd cells have a nominal cell potential of 1.2 volts (V). This is lower than the 1.5 V of alkaline and zinc–carbon primary cells, and consequently they are not appropriate as a replacement in all applications. However, the 1.5 V of a primary alkaline cell refers to its initial, rather than average, voltage. Unlike alkaline and zinc–carbon primary cells, a Ni–Cd cell's terminal voltage only changes a little as it discharges. Because many electronic devices are designed to work with primary cells that may discharge to as low as 0.90 to 1.0 V per cell, the relatively steady 1.2 V of a Ni–Cd cell is enough to allow operation. Some would consider the near-constant voltage a drawback as it makes it difficult to detect when the battery charge is low.
These batteries are more difficult to damage than other batteries, tolerating deep discharge for long periods. In fact, Ni–Cd batteries in long-term storage are typically stored fully discharged. This is in contrast, for example, to lithium ion batteries, which are less stable and will be permanently damaged if discharged below a minimum voltage.
Nickel–metal hydride (NiMH) batteries are the newest, and most similar, competitor to Ni–Cd batteries. Compared to Ni–Cd batteries, NiMH batteries have a higher capacity and are less toxic, and are now more cost effective. However, a Ni–Cd battery has a lower self-discharge rate (for example, 20% per month for a Ni–Cd battery, versus 30% per month for a traditional NiMH under identical conditions), although low self-discharge ("LSD") NiMH batteries are now available, which have substantially lower self-discharge than either Ni–Cd or traditional NiMH batteries. This results in a preference for Ni–Cd over non-LSD NiMH batteries in applications where the current draw on the battery is lower than the battery's own self-discharge rate (for example, television remote controls). In both types of cell, the self-discharge rate is highest for a full charge state and drops off somewhat for lower charge states. Finally, a similarly sized Ni–Cd battery has a slightly lower internal resistance, and thus can achieve a higher maximum discharge rate (which can be important for applications such as power tools).
Ni–Cd batteries may suffer from a "memory effect" if they are discharged and recharged to the same state of charge hundreds of times. The apparent symptom is that the battery "remembers" the point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged. The capacity of the battery is not actually reduced substantially. Some electronics designed to be powered by Ni–Cd batteries are able to withstand this reduced voltage long enough for the voltage to return to normal. However, if the device is unable to operate through this period of decreased voltage, it will be unable to get enough energy out of the battery, and for all practical purposes, the battery appears "dead" earlier than normal.
Ni–Cd batteries contain between 6% (for industrial batteries) and 18% (for consumer batteries) cadmium, which is a toxic heavy metal and therefore requires special care during battery disposal.
Their self-discharge rate is about 10% per month.
They can withstand about 2,000 cycles.
Each cell provides 1.2 V.
3 - Nickel Metal Hydride batteries: Newer rechargeable batteries used wherever a standard AA or AAA battery can be used.
The "metal" M in the negative electrode of a NiMH cell is actually 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, and/or aluminium. Very few cells use higher-capacity negative electrode materials based on AB2 compounds, where A is titanium and/or vanadium and B is zirconium or nickel, modified with chromium, cobalt, iron, and/or manganese, due to the reduced life performances.[11] Any of these compounds serve the same role, reversibly forming a mixture of metal hydride compounds.
The charging voltage is in the range of 1.4–1.6 V/cell. In general, a constant-voltage charging method cannot be used for automatic charging. When fast-charging, it is advisable to charge the NiMH cells with a smart battery charger to avoid overcharging, which can damage cells and even be dangerous.[13] A NiCd charger should not be used as a substitute for an automatic NiMH charger.
A fully charged cell supplies an average 1.25 V/cell during discharge, down 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). Under a light load (0.5 ampere), the starting voltage of a freshly charged AA NiMH cell in good condition is about 1.4 volts.
A complete discharge of a battery can result in one or more cells going into polarity reversal, which can cause permanent damage to those cells. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the good cells will start to drive the discharged cell in reverse, which can cause permanent damage to that cell.
NiMH cells historically 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 rate 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. So charge them and use them. Don't charge them and store them!
Improper disposal of NiMH batteries poses less environmental hazard than that of NiCd because of the absence of toxic cadmium. However, mining and processing the various alternate metals that form the negative electrode may pose other types of environmental impact, depending on the metal, mining method, and environmental practices of the mine.
Most industrial nickel is recycled, due to the relatively easy retrieval of the magnetic element from scrap using electromagnets, and due to its high value.
4 - Lithium-ion batteries: They power your phone, your laptop, your tablet... and some airplanes.
With a voltage of 3.7V per cell it is not suitable as a replacement for standard AA or AAA (1.5V) batteries.
They are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, no memory effect, and only a slow loss of charge when not in use.
The participants in the electrochemical reactions in a lithium-ion battery are the negative and positive electrodes with the electrolyte providing a conductive medium for Lithium-ions to move between the electrodes.
Both electrodes allow lithium ions to move in and out of their interiors. During insertion (or intercalation) ions move into the electrode. During the reverse process, extraction (or deintercalation), ions move back out. When a lithium-ion based cell is discharging, the positive Lithium ion moves from the negative electrode (usually graphite) and enters the positive electrode (lithium containing compound). When the cell is charging, the reverse occurs.
Batteries gradually self-discharge even if not connected and delivering current. Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month. The rate increases with temperature and state of charge. A 2004 study found that for most cycling conditions self-discharge was primarily time-dependent; however, after several months of stand on open circuit or float charge, state-of-charge dependent losses became significant. The self-discharge rate did not increase monotonically with state-of-charge, but dropped somewhat at intermediate states of charge. Self-discharge rates may increase as batteries age.
Rechargeable battery life is often stated in number of charge cycles, but depth of discharge is usually not explicitly stated. Apple Inc. clarify that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle.
Batteries may last longer if not stored fully discharged. As the battery self-discharges over time, its voltage gradually reduces. When depleted below the low-voltage threshold of the protection circuit (2.4 to 2.9 V/cell, depending on chemistry) it will be disabled and cannot be further discharged until recharged. This because as the discharge progresses, the metallic contents of the cell are plated onto its internal structure creating an unwanted discharge path. It is recommended to store batteries at 40% charge level.
Since Li-ion batteries contain no toxic metals (unlike other types of batteries which may contain lead or cadmium) they are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, but mining generally remains cheaper than recycling. At present, not much is invested into recycling Li-ion batteries due to costs, complexities and low yield.
The standard recommendation is to keep them charged, as close to 100% as possible. The circuitry will prevent recharge until its natural discharge rate reaches 95%, thus preventing the use of excessive recharge cycles, and keeping the battery always ready to operate when needed.
5 - Others... there are other rechargeable battery technologies, but they are less common and so beyond the scope of this thread.
