Batteries

For more information, see this article's corresponding Wikipedia page: Electric battery.

A nickel–cadmium Varta barrel battery that has leaked onto the mainboard of a Korg Poly-61, causing massive corrosion to circuit board traces and legs of integrated circuits.

A battery is a self-contained device that converts chemical chemical energy into a direct current by way of a redox reaction. It consists of one or more cells, the composition of which determines whether the battery is disposable (primary) or rechargeable (secondary). Batteries are typically opposed to mains power as a source of electrical energy, although the two are often used in tandem to power components within a piece of equipment.

In the context of repairing equipment, batteries can be problematic due to their propensity for leaking.

Battery Types and Risks

Disposable

Zinc–Carbon

Zinc–carbon was the first commercially available battery type and is still somewhat frequently used, although it has largely been replaced by the similarly composed alkaline battery. Like the alkaline battery, the zinc–carbon battery contains manganese dioxide and zinc electrodes. Unlike the alkaline battery, the zinc–carbon battery uses ammonium chloride as the electrolyte (zinc chloride in the case of "heavy-duty" zinc–carbon batteries), which is acidic.

Either when it has been completely consumed or after three to five years from its manufacture (its shelf life), a zinc–carbon battery is prone to leaking. The contents of the leakage may include manganese hydroxide, zinc ammonium chloride, ammonia, zinc chloride, zinc oxide, water and starch. None of these are particularly dangerous to human skin, but this combination of materials is corrosive to metals, such as those of the battery contacts and surrounding circuitry.

Online discussions suggest that zinc-carbon battery leakage can be effectively cleaned with baking soda.

Alkaline

Alkaline batteries use manganese dioxide and zinc electrodes with an electrolyte of potassium hydroxide. The alkaline battery gets its name from the replacement of the acidic ammonium chloride of zinc–carbon batteries with potassium hydroxide, which is an alkaline. Alkaline batteries are considerably more efficient, more environmentally friendly, and more shelf-stable than zinc–carbon batteries—five to ten years, when stored room temperature. Alkaline batteries largely replaced zinc-carbon batteries in regular use by 1990.

After an alkaline battery has been spent, or as it reaches the ends of its shelf life, the chemistry of its cells change, and hydrogen gas is generated as a byproduct. When enough pressure has been built up internally, the casing splits at the bases or side (or both), releasing manganese oxide, zinc oxide, potassium hydroxide, zinc hydroxide, and manganese hydroxide.

Alkaline battery leakage can be effectively neutralized with lemon juice or distilled white vinegar. Eye protection and rubber gloves should be worn, as the potassium hydroxide electrolyte is caustic.

Rechargable

Nickel–Cadmium (Ni-Cd)

Nickel–cadmium batteries use nickel oxide hydroxide and metallic cadmium electrodes with an electrolyte of potassium hydroxide. Sealed Ni-Cd batteries were widely used in photography equipment, handheld power tools, and radio-controlled toys from the early 1940s until the early 1990s, when nickel–metal hydride batteries supplanted them (like how alkaline batteries replaced zinc–carbon batteries). In computers, Ni-Cd batteries first saw use in the mid-1980s as a cheaper alternative to lithium batteries for powering real-time clocks and preserving BIOS settings. Nickel–cadmium batteries were also briefly used in laptop battery packs, until the advent of commercially viable nickel–metal hydride batteries in the early 1990s. Ni-Cd batteries are still used in some uninterruptible power supplies and emergency lighting setups.

Except in aeronautical or other high-risk applications, Ni-Cd batteries are intentionally not hermetically sealed and include pressure vents for safety if the batteries are charged improperly. The seal around the cell(s) is usually plastic heat-shrink tubing; with age and sufficient thermal cycles the seal will degrade and allow electrolyte to leak through. The leakage usually travels down the positive and/or negative terminals onto any surrounding circuitry (see the above image).

Like with alkaline battery leakage, Ni-Cd leakage can be effectively neutralized with lemon juice or distilled white vinegar.

Nickel–Metal Hydride (Ni-MH)

Nickel–metal hydride (Ni-MH) largely replaced Ni-Cd batteries in the early 1990s. They replaced the metallic cadmium electrode with a hydrogen-absorbing alloy, allowing it to have over two times the capacity of Ni-Cd batteries while being easier to recycle.

The practical shelf life of a Ni-MH is roughly five years. Cylindrical jelly-roll Ni-MH cells, like the ones used in 1990s laptop battery packs, discharge at a rate of up to 2% per day, while button cells like the ones used in motherboard batteries discharge at a rate of less than 20% per month. They are said to leak less frequently than an alkaline battery but have a similar failure mode.

Lithium

One of the first personal computers with a built-in lithium battery for this purpose was the original Macintosh from 1984.