nicad

A nicad is a rechargeable battery built from nickel oxide hydroxide positive plates, metallic cadmium negative plates, and potassium hydroxide electrolyte sealed in a steel case. The electrochemistry delivers roughly 1.2 volts per cell and holds charge far longer than older alkaline types when sitting idle. Nicads dominated portable tools, emergency lighting, and aircraft systems from the 1950s onward because they tolerate physical shock, vibration, and temperature swings that would kill other batteries.

The core advantage is robustness. A nicad survives thousands of charge cycles, performs at minus 20 degrees Celsius, and tolerates being left uncharged for months without permanent damage. This made them invaluable in military equipment, mining headlamps, and any tool destined for field work. A 1.2 amp-hour nicad cell weighs roughly 35 grams and measures about 50 millimeters tall and 17 millimeters in diameter in the standard cylindrical form, though button cells and rectangular industrial versions also exist.

The memory effect problem

Nicads introduced a notorious drawback called the memory effect. If you repeatedly recharged a partially discharged nicad before it fully depleted, the battery would eventually forget how to access its full capacity, behaving as though it held less charge than it actually did. This irritated consumers and drove engineers to develop nickel-metal hydride and lithium chemistries starting in the 1990s. Many workplaces responded by training operators to fully discharge nicads before recharging, an inconvenient workaround that persisted for decades.

Cadmium is toxic and accumulates in soil and water, which triggered environmental regulations across Europe and North America starting in the 2000s. That pressure killed consumer-grade nicads almost entirely. Industrial and military applications still use them, however, because no other rechargeable battery matches their cold weather resilience or tolerance for physical abuse at comparable cost. A nicad in a two-way radio or emergency lighting system may still outlast the equipment housing it.

Charging a nicad requires a current-limiting charger, typically delivering charge at 0.1 to 0.5 times the cell capacity in amp-hours. Fast chargers exist but risk thermal damage if the battery is already warm. The chemistry and form factor mean nicads sit uneasily in modern supply chains: still specified for critical backup power, yet increasingly difficult to source and dispose of legally.