Greenworks 80v string trimmer problem

[MowerMike]

It's less than a year old, bought the trimmer, battery and charger together. The battery has three green indicator lights and sometimes even with all three lit the trimmer will shut off after a few seconds. If I then put the battery back on charge and wait until the charger stops, put the battery back in the trimmer, the trimmer will continue to run. I think I just have to make sure I run the charger just before I'm ready to use the trimmer.

The charger should not continue to charge the battery if it is already showing that it is fully charged per the indicator lights. What it means is that the battery is weak, and not properly holding a charge. So, it looks like the battery is a dud, and you should be able to replace it under warranty.