Abattery produces , which is current that flows in only one direction.

The given blank can be filled with direct.

Explanation:

A battery refers to a chemical apparatus that is used to store electrical energy. A battery generates a direct current that is a current, which flows in only one direction. DC means direct current and it should exhibit fixed terminals, that is, negative and positive terminals, which cannot be altered.  

As the batteries have fixed content, they possess fixed terminals, thus, they can store only direct current. Thus, the batteries produce direct current and produce a voltage in only one direction, and they exhibit a polarity of negative and positive.