My Milwaukee m18 fuel quik lock string trimmer has melted the negatives on two of my 8.0ah batteries as well. While using the string trimmer id get around 30-40 minutes of use. And the first two times i used it the batteries got extremely hot after use and had to cool off before charging. They still work and i havent encountered a issue since. The plastic is not nearly as bad as pictures posted in this thread though. I bought my string trimmer two months ago and use it weekly and just noticed the damaged terminal after using my circ saw