The weight of nickel - cadmium energy storage batteries is an important consideration in many applications, especially those where portability or weight - to - energy ratio matters. Ni - Cd batteries are relatively heavy compared to some modern battery chemistries, such as lithium - ion batteries.

The main reason for the relatively high weight of Ni - Cd batteries is the use of cadmium in the negative electrode. Cadmium is a dense metal, and its presence in the battery contributes significantly to the overall weight. For example, a typical Ni - Cd battery with a capacity of 1000 mAh may weigh around 50 - 80 grams, while a lithium - ion battery with a similar capacity can be much lighter, often weighing only 20 - 30 grams.

This relatively high weight limits the use of Ni - Cd batteries in some applications where portability is a key factor, such as in mobile phones and lightweight portable electronics. In these devices, the trend has shifted towards lighter lithium - ion batteries to reduce the overall weight of the product and improve user experience.

However, in some industrial and stationary applications, the weight of the battery may not be as critical as other factors. For example, in large - scale energy storage systems for power grids or in some industrial backup power supplies, the focus is more on the battery's capacity, reliability, and cost - effectiveness. In these cases, Ni - Cd batteries can still be a viable option despite their relatively high weight, as they offer advantages such as high overcharge tolerance and long - term stability.

Moreover, in some applications where the battery is installed in a fixed location and does not need to be moved frequently, the weight of the Ni - Cd battery may not be a major drawback. For instance, in emergency power systems for buildings, the weight of the Ni - Cd battery is less of a concern compared to its ability to provide reliable backup power during outages.