Nickel - cadmium energy storage batteries are well - known for their relatively high overcharge tolerance. Overcharging occurs when a battery is charged beyond its full - charge state. In many battery chemistries, overcharging can lead to serious problems, such as overheating, gas evolution, and even battery explosion. However, Ni - Cd batteries have some built - in mechanisms that allow them to withstand a certain degree of overcharging.

One of the main reasons for the overcharge tolerance of Ni - Cd batteries is the oxygen - recombination reaction that occurs within the battery during overcharging. When the positive electrode is fully charged, oxygen is generated. In a Ni - Cd battery, this oxygen can diffuse to the negative electrode and react with the cadmium, recombining to form cadmium hydroxide. This reaction consumes the oxygen and prevents the build - up of excessive gas pressure inside the battery.

This overcharge tolerance makes Ni - Cd batteries suitable for applications where precise charge control is difficult or not always possible. For example, in some industrial backup power systems, the charging process may not be constantly monitored, and Ni - Cd batteries can tolerate occasional overcharging without significant damage. In addition, in some simple consumer electronics devices that do not have sophisticated charging management circuits, Ni - Cd batteries can also be a reliable choice due to their overcharge - resistant nature.

However, it should be noted that although Ni - Cd batteries have good overcharge tolerance, continuous and excessive overcharging can still have a negative impact on their lifespan. Prolonged overcharging can cause the electrodes to degrade gradually, reducing the overall capacity and performance of the battery over time. Therefore, even though Ni - Cd batteries are more forgiving in terms of overcharging compared to some other batteries, it is still advisable to use proper charging methods and charging management systems to ensure their long - term reliability and performance.