Thread: How does a battery die

  1. #1

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    May 2005

    How does a battery die

    A battery keeps a potential difference via the electromotive force (EMF) which is usually just some sort of chemical that maintains the voltage across the terminals such that a current can flow. The actual potential is:

    EMF - Ir where r is the bit of resistance innate to the battery. I asked a physics professor what actually happens when a battery dies, and he said that it is due to the internal resistance eventually skyrocketing, but he couldn't explain further. Does anybody know any more about what's actually going on with the internal resistance when a battery dies?
    I'm not immature, I'm refined in the opposite direction.

  2. #2
    Ethernal Noob
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    With honor.

  3. #3
    verbose cat
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    Quote Originally Posted by indigo0086 View Post
    With honor.
    Not necessarily. You should hear some of my kids' toys when the batteries die. They're anything but honorable... Mickey Mouse sounds positively demonic!
    abachler: "A great programmer never stops optimizing a piece of code until it consists of nothing but preprocessor directives and comments "

  4. #4
    Registered User hk_mp5kpdw's Avatar
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    From Wikipedia entry:
    Life of primary batteries

    Even if never taken out of the original package, disposable (or "primary") batteries can lose 8 to 20 percent of their original charge every year at a temperature of about 20°–30°C.[48] This is known as the "self discharge" rate and is due to non-current-producing "side" chemical reactions, which occur within the cell even if no load is applied to it. The rate of the side reactions is reduced if the batteries are stored at low temperature, although some batteries can be damaged by freezing. High or low temperatures may reduce battery performance. This will affect the initial voltage of the battery. For an AA alkaline battery this initial voltage is approximately normally distributed around 1.6 volts.

    Life of rechargeable batteries

    Rechargeable batteries traditionally self-discharge more rapidly than disposable alkaline batteries; up to three percent a day (depending on temperature). However, modern Lithium designs have reduced the self-discharge rate to a relatively low level (but still poorer than for primary batteries). Due to their poor shelf life, rechargeable batteries should not be stored and then relied upon to power flashlights or radios in an emergency. For this reason, it is a good idea to keep alkaline batteries on hand. NiCd Batteries are almost always "dead" when purchased, and must be charged before first use.

    Although rechargeable batteries may be refreshed by charging, they still suffer degradation through usage. Low-capacity Nickel Metal Hydride (NiMH) batteries (1700-2000 mAh) can be charged for about 1000 cycles, whereas high capacity NiMH batteries (above 2500 mAh) can be charged for about 500 cycles.[49] Nickel Cadmium (NiCd) batteries tend to be rated for 1,000 cycles before their internal resistance increases beyond usable values. Normally a fast charge, rather than a slow overnight charge, will result in a shorter battery lifespan.[49] However, if the overnight charger is not "smart" (i.e. it cannot detect when the battery is fully charged), then overcharging is likely, which will damage the battery.[50] Degradation usually occurs because electrolyte migrates away from the electrodes or because active material falls off the electrodes. NiCd batteries suffer the drawback that they should be fully discharged before recharge. Without full discharge, crystals may build up on the electrodes, thus decreasing the active surface area and increasing internal resistance. This decreases battery capacity and causes the dreaded "memory effect". These electrode crystals can also penetrate the electrolyte separator, thereby causing shorts. NiMH, although similar in chemistry, does not suffer from ‘memory effect’ to quite this extent.[51]

    Automotive lead-acid rechargeable batteries have a much harder life. Because of vibration, shock, heat, cold, and sulfation of their lead plates, few automotive batteries last beyond six years of regular use. Automotive starting batteries have many thin plates to provide as much current as possible in a reasonably small package. Typically they are only drained a small amount before recharge. Care should be taken to avoid deep discharging a starting battery, since each charge and discharge cycle causes active material to be shed from the plates. Hole formation in the plates leads to less surface area for the current-producing chemical reactions, resulting in less available current when under load. Leaving a lead-acid battery in a deeply discharged state for any significant length of time allows the lead sulfate to crystallize, making it difficult or impossible to remove during the charging process. This can result in a permanent reduction in the available plate surface, and therefore reduced current output and energy capacity.

    "Deep-Cycle" lead-acid batteries such as those used in electric golf carts have much thicker plates to aid their longevity. The main benefit of the lead-acid battery is its low cost; the main drawbacks are its large size and weight for a given capacity and voltage. Lead-acid batteries should never be discharged to below 20% of their full capacity, because internal resistance will cause heat and damage when they are recharged. Deep-cycle lead-acid systems often use a low-charge warning light or a low-charge power cut-off switch to prevent the type of damage that will shorten the battery's life.

    Special "reserve" batteries intended for long storage in emergency equipment or munitions keep the electrolyte of the battery separate from the plates until the battery is activated, allowing the cells to be filled with the electrolyte. Shelf times for such batteries can be years or decades. However, their construction is more expensive than more common forms.

    Extending battery life

    Battery life can be extended by storing the batteries at a low temperature, as in a refrigerator or freezer, because the chemical reactions in the batteries are slower. Such storage can extend the life of alkaline batteries by ~5%; while the charge of rechargeable batteries can be extended from a few days up to several months.[52] In order to reach their maximum voltage, batteries must be returned to room temperature; therefore, alkaline battery manufacturers like Duracell do not recommend refrigerating or freezing batteries.[53]
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
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  5. #5
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    Quote Originally Posted by jEssYcAt View Post
    Not necessarily. You should hear some of my kids' toys when the batteries die. They're anything but honorable... Mickey Mouse sounds positively demonic!
    They slay their captors, and leave this world. The Screams of Mickey the Mighty Herald their Ascension into Batteryhalla.

  6. #6
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    I'm learning about a little electrochemistry in general chem right now. That wikipedia entry is unsatisfying, it doesn't really talk about what's going on. Look up "Redox" instead.

    Basically, the battery runs out when energy stored in the chemicals does also. Ever hear of conservation of energy? The thing where those scientists say that energy is never created or destroyed? Well energy is stored in chemical structures too, it just has a different form than, say, voltage.

  7. #7
    Officially An Architect brewbuck's Avatar
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    In a chemical battery energy exists in the form of different ions and electrons separated from each other by a gel or held in place by the work function of a metal plate. As the battery discharges, the ions and electrons migrate toward regions of the battery with opposite charge and a current flows due to this movement of ions. Eventually, the ions end up in a configuration of lower energy than before, and they don't want to move any more, and so there is no more current.

  8. #8
    Registered User kryptkat's Avatar
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    Dec 2002
    Ok I got lost in all the fluff the wiki entry which did not say why batteries stop working.

    the ions and electrons migrate toward regions of the battery with opposite charge and a current flows due to this movement of ions. Eventually, the ions end up in a configuration of lower energy than before, and they don't want to move any more, and so there is no more current.
    nice try but also did not say why batteries stop working.

    A lead acid type that uses a sulfuric acid solution as an electrical conduate. The battery consisting of two electrodes of different materials one copper and the other zinc. <or can be a positively doped and negatively doped material such as lead> I will use copper and zinc for the example. But they can be any two different metals. In large plate form for maximum surface area. Dipped in the acid solution. As soon as that happens the electrons flow. The electrons use the h2so4 sulfuric acid to create ions from atoms of the compound solution. The ion missing an electron is the positive one and attracted to the negative terminal or electrode. So the one ion containing an extra electron is now negatively charged and attracted to the positive terminal. When you complete the circuit you power something. Potential energy of the battery.

    Happens when all the ions are separated thus no more electrons can flow. To undo this a positive charge higher than the batteries potential is applied thus forcing all the ions negatively charged off of the positive terminal and all the positively charged ions repelled off of the negative terminal. And that would be a recharge to restore initialized state.

    Other factors. Solution loss or evaporation from heat or electrolysis. Terminals decay. Cold temps. Etc.

    the batteries energy is the same.... it is just a matter of being able to conduct the electrons. meow!

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