The Rifle Regiment is currently categorized under "Category: Miles' Regiment, Pennsylvania Militia, American Revolution." That is the category you should use for a person who served in the 2nd Battalion of the Rifle Regiment.
2nd Battalion, Berks County Militia is a different regiment, and probably not the one you want to use. (No category currently exists for 2nd Battalion, Berks County Militia, but we could create one, given a profile that needs it.)
Betty Norman