You Do Need power plug adapter while traveling from Nauru to Botswana.

Here is Why You Need An Adapter

The outlet and plug type used in Botswana are D and G and in Nauru is I. This is how they look like.

Nauru

In Nauru, outlets of type I are in use.

Type I

Botswana

In Botswana, outlets of type D and G are in use.

Type D

Type G