I was pleasantly surprised at the power the m18 trimmer and hedge trimmer have. Can get about 45 min of string trimming out of a 9ah battery. Its light, its quiet, and man no vibration is nice on the old nerves.
Stihl seems to be further along with their backpack battery system using 21700 format cells and powerheads/hedge trimmers etc for commercial operation. But certainly there's ego etc that are also in that field.