A NiCd (nickel-cadmium) battery is a rechargeable battery that uses nickel for its positive electrode and cadmium for its negative electrode, with an alkaline solution as the liquid between them. Each cell produces 1.2 volts. Though largely replaced by newer chemistries in consumer electronics, NiCd batteries remain the go-to choice in aviation, railways, and industrial backup systems where reliability under harsh conditions matters more than energy density.
How a NiCd Battery Works
Inside every NiCd cell, two metal-based plates sit in a potassium hydroxide solution. When you use the battery, the nickel plate absorbs electrons and water, converting to a different form of nickel while releasing charged particles into the solution. Simultaneously, the cadmium plate gives up electrons, which flow through your device as electrical current. Charging reverses the whole process, restoring both plates to their original state.
This chemistry is remarkably stable. Unlike lithium-ion cells, which need built-in protection circuits to prevent overheating or voltage spikes, NiCd cells tolerate overcharging, deep discharging, and high currents without catastrophic failure. That inherent ruggedness is the reason the technology has persisted for decades despite its lower energy capacity.
Energy Density and Performance
NiCd batteries store between 40 and 75 watt-hours per kilogram, depending on the design. That’s significantly less than lithium-ion (which typically ranges from 150 to 250 Wh/kg), meaning NiCd packs are heavier for the same amount of stored energy. For portable consumer gadgets where weight and size matter, this is a real disadvantage.
Where NiCd excels is in delivering energy quickly and consistently. Its internal resistance is lower than both nickel-metal hydride (NiMH) and lithium-ion in comparable pack sizes, typically 100 to 200 milliohms for a 6-volt pack. Lower resistance means the battery can supply high bursts of current without significant voltage drop, which is why NiCd powered cordless power tools for years before lithium-ion caught up.
The Memory Effect
NiCd batteries are famous for the “memory effect,” a real but often exaggerated problem. If you repeatedly recharge a NiCd battery before it’s fully drained, it can gradually lose usable capacity. The battery “remembers” the shorter discharge cycle and behaves as though it’s empty at that point, even though chemical energy remains.
The fix is straightforward: periodically discharge the battery fully under controlled conditions, then recharge it completely. A cell is considered fully discharged when it drops to about 1.0 to 1.1 volts. This cycling process prevents the crystalline buildup on the cadmium plate that causes the capacity loss. It’s also good practice to slow-charge NiCd batteries at the overnight rate roughly every five fast charges, which helps stabilize the cells and extend their lifespan.
Where NiCd Batteries Are Still Used
Consumer use has dropped sharply, but NiCd remains the preferred battery technology in several demanding industries. Aviation relies heavily on NiCd for aircraft starting and emergency systems. Railways and metro systems use them for backup power that keeps emergency braking, coach lighting, and driver-to-passenger communication running if the main power fails. Nuclear power plants, steel mills, offshore oil platforms, hospitals, and lighthouses all use NiCd for backup and emergency systems.
The reasons come down to a few qualities no other battery chemistry fully matches. NiCd cells handle extreme temperature swings with limited performance loss. They withstand vibrations, shocks, and electrical abuse that would destroy other batteries. They last three to five times longer than equivalent lead-acid batteries, often reaching 2,000 to 2,500 charge cycles. And critically, they lose capacity gradually rather than dying suddenly, which allows maintenance teams to replace them before they actually fail. In a nuclear plant or an aircraft, that predictability is worth more than energy density.
How NiCd Compares to NiMH and Lithium-Ion
NiMH batteries were the first major replacement for NiCd in consumer products. They offer higher energy density, contain no toxic heavy metals, and largely eliminated the memory effect. NiMH costs about 20% more than NiCd upfront, and its cost per charge cycle is roughly three times higher ($0.12 versus $0.04). NiMH also has higher internal resistance, which means it can’t deliver peak current quite as effectively.
Lithium-ion took things further with dramatically higher energy density and no memory effect at all. But lithium-ion packs cost about 40% more than NiCd to manufacture and require embedded protection circuits to monitor voltage and current, since the chemistry can become unsafe if overcharged or punctured. That added electronic management system is itself a potential point of failure, which is one reason high-reliability industries still prefer NiCd. For everyday use in phones, laptops, and modern power tools, lithium-ion is the clear winner. For a backup system in a hospital or on an oil rig that needs to sit for months and then work perfectly, NiCd still has an edge.
The Cadmium Problem
The biggest strike against NiCd is environmental. Cadmium is a toxic heavy metal that accumulates in soil and water and poses serious health risks with long-term exposure. The European Union’s RoHS directive restricts cadmium in electronics to just 0.01% by weight (100 parts per million), effectively banning NiCd from most consumer products sold in Europe. Many other regions have followed with similar restrictions.
NiCd batteries should never go in household trash. Most countries require them to be collected and recycled separately. The cadmium can be recovered and reused, but only if the batteries actually reach a recycling facility. This disposal burden is a major reason manufacturers shifted to NiMH and lithium-ion for anything a consumer might eventually throw away. Industrial NiCd batteries, used in controlled settings with professional maintenance and recycling programs, face fewer regulatory barriers since their disposal chain is more predictable.
Maintenance Tips for NiCd Batteries
If you still use NiCd batteries in power tools, RC vehicles, or emergency equipment, a few habits will keep them performing well. Cycle them fully (discharge, then recharge) on a regular basis to prevent memory effect. Don’t leave them on a fast charger indefinitely. Use a slow overnight charge every five cycles or so to equalize the cells and maintain full capacity.
You can check a NiCd battery’s remaining capacity by discharging it at a known, constant rate and timing how long it takes to reach 1.0 to 1.1 volts per cell. Multiply the discharge current by the time, and you have the actual capacity in milliamp-hours. If that number has dropped significantly from the battery’s rating, cycling may bring some of it back. If not, it’s time for a replacement.