First, let me start off by saying that this is a powerful tool, for a battery operated trimmer. In fact, it is the only .080 dual-line battery operated trimmer that I have ever seen. And, it is powerful enough to cut through almost any kind of overgrowth. However, I did have a problem that caused me to return the trimmer (actually two trimmers since I returned my first trimmer for an exchange and then had to return the replacement trimmer for a refund).
The first trimmer worked just fine for about 15 minutes. I was trimming along a fence, when it suddenly stopped working without any warning. After an overnight battery charge, I tried to use the trimmer again. At that point, it would only beep and the trimmer head would not turn. And, after holding down the trigger for a few seconds, the battery started smoking. Needless to say, I immediately called Amazon and requested a replacement. Amazon Customer Service was very helpful and walked me though the return process. I decided on a replacement rather than a refund, since trimmer (while it was working) was exactly what I had been looking for.
I received my replacement trimmer the very next week. I was very careful with that trimmer and it lasted almost two weeks. During those two weeks, I trimmed using the slowest speed possible. Under those conditions, I did not experience any problems whatsoever. However, at the end of the two weeks when I was trimming along the fence again, the trimmer stopped working. I charged the trimmer battery overnight, but it never worked again. That trimmer went back for a refund.
Both times when the trimmers died, I was trimming at about 1/2 to 3/4 full speed continuously for about 5-10 minutes. It is my impression that Black and Decker did not take into account the amount of current that would flow through the battery if someone used the trimmer like they would a gas trimmer. With both of my trimmers, the battery seems to have completely shorted out (that, or or the trimmer motor burned out). If you use the trimmer at slow speeds or don't continuously use higher speeds, you should be ok. But, if you decide to use the trimmer at higher speeds continuously for any length of time, you may experience a problem. I think Black and Decker should have installed a circuit breaker or fuse between the battery pack and the motor.