Have had the issue with both my gas and my battery(I have a good one)trimmer......In my experience that depends on the string trimmer. I have an electric one and yep, the fence eats the string. It only runs about 20 minutes before a 40+ minute recharge. I'd never get the fence trimmed at that rate. My gas trimmer will rip the same welded wire fence like paper. TSC 2x4 welded wire fence. It is on the inside of the north fence line which is hotwire on the outside. I had the welded wire from some other project so I used it to keep the chickens on the inside.
...it's all about technique