question: Why do batteries leak that white powdery stuff and how can it be prevented?
comment: Batteries leak when they are over discharged. You can prevent this by changing them when they are below their listed minimum voltage, when they stop working. If you continue to drain them, the electrolyte can expand and force itself past the seal. When it dries, you see that white residue. It's quite corrosive before it drys, and it can damage your gadget. Whenever you store a gadget, you should take out the batteries.
passages: Once a leak has formed due to corrosion of the outer steel shell, potassium hydroxide absorbs carbon dioxide from the air to form a feathery crystalline structure of potassium carbonate that grows and spreads out from the battery over time, following along metal electrodes to circuit boards where it commences oxidation of copper tracks and other components, leading to permanent circuitry damage.
  
  The leaking crystalline growths can also emerge from seams around battery covers to form a furry coating outside the device, that corrodes any objects in contact with the leaking device.
  
  Section::::Disposal.
   Many battery chemicals are corrosive, poisonous or both. If leakage occurs, either spontaneously or through accident, the chemicals released may be dangerous. For example, disposable batteries often use a zinc "can" both as a reactant and as the container to hold the other reagents. If this kind of battery is over-discharged, the reagents can emerge through the cardboard and plastic that form the remainder of the container. The active chemical leakage can then damage or disable the equipment that the batteries power. For this reason, many electronic device manufacturers recommend removing the batteries from devices that will not be used for extended periods of time.
   Disposing of a battery via incineration may cause an explosion as steam builds up within the sealed case.
  
  Recalls of devices using Lithium-ion batteries have become more common in recent years. This is in response to reported accidents and failures, occasionally ignition or explosion. An expert summary of the problem indicates that this type uses "liquid electrolytes to transport lithium ions between the anode and the cathode. If a battery cell is charged too quickly, it can cause a short circuit, leading to explosions and fires".
  
  Section::::Hazards.:Leakage.
   The reason for leaks is that as batteries discharge — either through usage or gradual self-discharge — the chemistry of the cells changes and some hydrogen gas is generated. This out-gassing increases pressure in the battery. Eventually, the excess pressure either ruptures the insulating seals at the end of the battery, or the outer metal canister, or both. In addition, as the battery ages, its steel outer canister may gradually corrode or rust, which can further contribute to containment failure.
   Most battery chemistries have less dramatic, and less dangerous, failure modes. The chemicals in most batteries are often toxic to some degree, but are rarely explosive or flammable; many are corrosive, which accounts for advice to avoid leaving batteries inside equipment for long periods as the batteries may leak and damage the equipment. Lead acid batteries are an exception, for charging them generates hydrogen gas, which can explode if exposed to an ignition source (e.g., a lit cigarette or some such) and such an explosion will spray sulfuric acid in all directions. Since this is corrosive and potentially blinding, this is a particular danger.
   The cells of VRLA batteries typically swell when the internal pressure rises, so giving a warning to users and mechanics. The deformation varies from cell to cell, and is greatest at the ends where the walls are unsupported by other cells. Such over-pressurized batteries should be carefully isolated and discarded. Personnel working near batteries at risk for explosion should protect their eyes and exposed skin from burns due to spraying acid and fire by wearing a face shield, overalls, and gloves. Using goggles instead of a face shield sacrifices safety by leaving the face exposed to possible flying acid, case or battery fragments, and heat from a potential explosion.
   Disk batteries, also called button cells, are often mistakenly ingested, particularly by children and the elderly. They may be mistaken for a medication pill because of their size and shape, or they may be swallowed after being held in the mouth while the battery is being changed. Battery ingestion can cause medical problems including blocked airway, vomiting, irritability, persistent drooling, and rash (due to nickel metal allergy).
  
  Section::::Abnormal ingestion.
   Lithium batteries can provide extremely high currents and can discharge very rapidly when short-circuited. Although this is useful in applications where high currents are required, a too-rapid discharge of a lithium battery can result in overheating of the battery, rupture, and even an explosion. Lithium-thionyl chloride batteries are particularly susceptible to this type of discharge. Consumer batteries usually incorporate overcurrent or thermal protection or vents to prevent an explosion.
  
  Section::::Safety issues and regulation.:Air travel.
   Alkaline batteries are prone to leaking potassium hydroxide, a caustic agent that can cause respiratory, eye and skin irritation. Risk of this can be reduced by not attempting to recharge disposable alkaline cells, not mixing different battery types in the same device, replacing all of the batteries at the same time, storing in a dry place and at room temperature, and removing batteries for storage of devices.
   When handled improperly, or if manufactured defectively, some rechargeable batteries can experience thermal runaway resulting in overheating. Sealed cells will sometimes explode violently if safety vents are overwhelmed or nonfunctional. Especially prone to thermal runaway are lithium-ion batteries, most markedly in the form of the lithium polymer battery. Reports of exploding cellphones occasionally appear in newspapers. In 2006, batteries from Apple, HP, Toshiba, Lenovo, Dell and other notebook manufacturers were recalled because of fire and explosions. The Pipeline and Hazardous Materials Safety Administration (PHMSA) of the U.S. Department of Transportation has established regulations regarding the carrying of certain types of batteries on airplanes because of their instability in certain situations. This action was partially inspired by a cargo bay fire on a UPS airplane.
   The operating life of a zinc–air cell is a critical function of its interaction with its environment. The electrolyte loses water more rapidly in conditions of high temperature and low humidity. Because the potassium hydroxide electrolyte is deliquescent, in very humid conditions excess water accumulates in the cell, flooding the cathode and destroying its active properties. Potassium hydroxide also reacts with atmospheric carbon dioxide; carbonate formation eventually reduces electrolyte conductivity. Miniature cells have high self-discharge once opened to air; the cell's capacity is intended to be used within a few weeks.
  
  Section::::Discharge properties.
   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 in a digital camera, where one 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/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.
   The batteries used consisted respectively of forty, forty-three, and forty-four cells of zinc and carbon, or nine hundred and sixty cells in all, divided into twenty-three distinct batteries, each battery to fire a hundred and sixty fuses, arranged in divided circuit, in eight groups of twenty each. The fluid was made in the proportion of six pounds of bichromate of potassa, one gallon concentrated pure English sulphuric acid, and three gallons of water. 
   The deep discharge testing is itself damaging to batteries due to the chemicals in the discharged battery starting to crystallize into highly stable molecular shapes that will not re-dissolve when the battery is recharged, permanently reducing charge capacity. In lead acid batteries this is known as sulfation but also affects other types such as nickel cadmium batteries and lithium batteries. Therefore, it is commonly recommended that rundown tests be performed infrequently, such as every six months to a year.
  
  Section::::Batteries.:Testing of strings of batteries/cells.
   Primary batteries readily available to consumers range from tiny button cells used for electric watches, to the No. 6 cell used for signal circuits or other long duration applications. Secondary cells are made in very large sizes; very large batteries can power a submarine or stabilize an electrical grid and help level out peak loads.
  
  Section::::Hazards.
  
  Section::::Hazards.:Explosion.
  
  A battery explosion is generally caused by misuse or malfunction, such as attempting to recharge a primary (non-rechargeable) battery, or a short circuit.
   Lithium-ion batteries may suffer thermal runaway and cell rupture if overheated or overcharged, and in extreme cases this can lead to combustion. To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that shuts down the battery when its voltage is outside the safe range. When handled improperly, or if manufactured defectively, some rechargeable batteries can experience thermal runaway resulting in overheating. Sealed cells will sometimes explode violently if safety vents are overwhelmed or nonfunctional. Reports of exploding cellphones have been published in newspapers. In 2006, batteries from Apple, HP, Toshiba, Lenovo, Dell and other notebook manufacturers were recalled because of fire and explosions.
   Zinc carbon cells have a short shelf life as the zinc is attacked by ammonium chloride. The zinc container becomes thinner as the cell is used, because zinc metal is oxidized to zinc ions. When the zinc case thins enough, zinc chloride begins to leak out of the battery. The old dry cell is not leak proof and becomes very sticky as the paste leaks through the holes in the zinc case. The zinc casing in the dry cell gets thinner even when the cell is not being used, because the ammonium chloride inside the battery reacts with the zinc. An "inside-out" form with a carbon cup and zinc vanes on the interior, while more leak resistant, has not been made since the 1960s.
   Some battery manufacturers include a built-in hydrometer to show the state of charge of the battery.
  
  The primary wear-out mechanism is the shedding of active material from the battery plates, which accumulates at the bottom of the cells and which may eventually short-circuit the plates. This can be substantially reduced by enclosing one set of plates in plastic separator bags, made from a permeable material. This allows the electrolyte and ions to pass through but keeps the sludge build up from bridging the plates.
  
  Section::::Environmental impact.
   Carriage and shipment of some kinds of lithium batteries may be prohibited aboard certain types of transportation (particularly aircraft) because of the ability of most types of lithium batteries to fully discharge very rapidly when short-circuited, leading to overheating and possible explosion in a process called thermal runaway. Most consumer lithium batteries have built-in thermal overload protection to prevent this type of incident, or are otherwise designed to limit short-circuit currents. Internal shorts from manufacturing defect or physical damage can lead to spontaneous thermal runaway.
  
  Section::::See also.
  
  BULLET::::- List of countries by lithium production
  
  BULLET::::- Lithium as an investment
   Starting batteries are of lighter weight than deep cycle batteries of the same size, because the thinner and lighter cell plates do not extend all the way to the bottom of the battery case. This allows loose disintegrated material to fall off the plates and collect at the bottom of the cell, prolonging the service life of the battery. If this loose debris rises enough it may touch the bottom of the plates and cause failure of a cell, resulting in loss of battery voltage and capacity.
  
  Section::::Cycles.:Deep-cycle batteries.
   The presence of such mobile carriers in the oxides triggers numerous physical damage processes that can drastically change the device characteristics over prolonged periods. The accumulation of damage can eventually cause the circuit to fail as key parameters such as threshold voltage shift due to such damage. The accumulation of damage resulting degradation in device behavior due to hot carrier injection is called “hot carrier degradation”.
   If the battery is over-filled with water and electrolyte, thermal expansion can force some of the liquid out of the battery vents onto the top of the battery. This solution can then react with the lead and other metals in the battery connector and cause corrosion.
  
  The electrolyte can seep from the plastic-to-lead seal where the battery terminals penetrate the plastic case.
  
  Acid fumes that vaporize through the vent caps, often caused by overcharging, and insufficient battery box ventilation can allow the sulfuric acid fumes to build up and react with the exposed metals.
  
  Section::::Maintenance precautions.
   Membranes are often the most costly and least reliable components of batteries, as they can be corroded by repeated exposure to certain reactants. The absence of a membrane enables the use of a liquid bromine solution and hydrogen: this combination is problematic when membranes are used, because they form hydrobromic acid that can destroy the membrane. Both materials are available at low cost.
   All batteries gradually self-discharge (whether installed in a device or not) and dead batteries will eventually leak. Extremely high temperatures can also cause batteries to rupture and leak (such as in a car during summer) as well as decrease the shelf life of the battery.
   Section::::Associated batteries.
  