Here's why:

* Lightweight: Aluminum is very light, which is important for portable batteries.

* Corrosion Resistance: Aluminum is resistant to corrosion, which is important for batteries that may be exposed to moisture or other corrosive elements.

* Good Electrical Conductivity: Aluminum is a good conductor of electricity, which helps to transfer current efficiently within the battery.

* Recyclable: Aluminum is highly recyclable, making it an environmentally friendly choice.

However, other non-ferrous metals like steel (often coated with tin or zinc) are also sometimes used for battery containers, particularly for larger batteries. The specific choice of metal depends on the type of battery, its intended use, and cost considerations.