Batteries power everything from cars to flashlights. But batteries do not last forever, even rechargeable ones, and occasionally "run down." In order to understand why batteries do this, it is important to understand how batteries generate energy in the first place.
Function
Batteries generate electricity through the controlled reactions of chemicals. Crude batteries can be created out of copper, lead and any acid (such as lemon juice or sulfuric acid). The acid and lead interact, releasing ions which are captured through the copper and become electricity. Powerful batteries have very strong chemicals within them to create energetic reactions within them and thus large amounts of electricity.
Time Frame
Chemical reactions are constantly flowing back and forth as chemical bonds are broken (which releases energy) and reformed (which takes energy). Over time, the energy generated by the breaking of chemical bonds is equaled by the energy used to create new bonds. This can be observed as a battery weakens over time. As the chemical reaction reached equilibrium (the point at which the reactions' energies are equal to is consumption), the battery "dies" or "runs down."
Significance
Because copper allows energy (in the form of electricity) to escape the battery, the more a battery is used, the quicker the reaction reaches equilibrium. To put it another way, if breaking a chemical bond gives you five pennies, but making a chemical bond costs four pennies, you have a surplus of pennies stored in your bank. If you spend some of those pennies, you have less to form new chemical bonds with and eventually, you will only have enough pennies to create bonds no matter how many you break. The analogy is incomplete, however, as no matter whether you spend the pennies or not, there will be a time at which the amount of pennies made equals the amount of pennies spent.
Identification
Rechargeable batteries reverse the basic battery operation occasionally and introduce energy (in the form of electricity applied through a recharger) back into the chemical reaction. After a while, however, the ability of the chemical reaction to absorb this extra energy is negated as the chemical reaction reaches equilibrium. Thus, rechargeable batteries are slightly less effective after their first recharge, slightly less after their second, and so on until the battery "dies" or is completely "run down." Granted, it takes significantly longer for rechargeable batteries to "run down" than standard batteries, but eventually the chemical reaction within will reach equilibrium eventually.
Warning
Do not attempt to recharge standard batteries. The typical standard battery configuration is not meant to be recharged and it may cause a fire, damage the recharger, or even explode spraying acid. Similarly, different rechargeable batteries use different chemicals, Nickle Metal Hydride (NiMH) or the older Nickle Cadmium (NiCad), and require different transfers of power to recharge properly. At best, a rechargeable battery which is recharged the wrong way will do nothing. At worst, it may explode, overheat, and start a fire.
All batteries should be disposed of properly as they contain toxic chemicals such as lead, nickle, lithium, or zinc. These chemicals may be small in amount, but in quantity can contaminate the soil and drinking water of wherever they are dumped. Check to see if your local community has a battery recycling program or a hazardous waste (or even "E-Waste") reclamation program. Some retailers allow for the proper disposal of batteries through recycling bins in their stores. Car batteries, for the most part, include a "deposit" when purchased which can be recovered when a run down battery is returned to the auto parts store. This is to encourage recycling since a typical car battery has several pounds of highly-toxic lead within it.
Tags: chemical reaction, chemical bonds, rechargeable batteries, after their, amount pennies, battery dies