Nickel–cadmium batteries (Ni-Cd) 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 personal 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. 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 top image).
Like with alkaline battery leakage, Ni-Cd leakage can be effectively neutralized with lemon juice or distilled white vinegar.