I have a B&D 18V hedge trimmer and it doe sgood job on our hedges, which are Pittosporum, Photinia and Griselinia (all reasonably soft wood). It will cut through finger-thickness branches. The line trimmer in the same series is fine for the lawn edges and light weeds. I wouldn't use it for anything more serious.
I've noticed some of the council guys in Nelson are now using heavier duty battery powered line trimmers etc. They look husky or stihl.