I've done a quick bit of digging and I believe that Charles Barracks were located in the SE outskirts of Braunschweig in Rautheimer Straße, where they seem still to stand.
They comprised the former Hindenburg Kaserne and possibly included the adjacent Heinrich-der-Loewe Kaserne.
It appears that Norwegian Army occupation forces were based there for a short period around 1948 (who referred to it as Vika Camp) and that they were handed back to the Bundeswehr sometime around 1958.
The site will be included on the Google Earth page in due course.
I've no idea which British units were based there. Perhaps others will be able to enlighten or correct.
Flash