Hello lbtd.

We are sorry to hear about your experience. There are three main reasons for a chain to come off: Incorrect bar or both chain for the saw; check to be sure that you are using the proper chain pitch, gauge and number of drive links to match the guide bar. Chain not properly tensioned; It is normal for a chain to stretch and require frequent adjustment. Chains should be tensioned before use. Check intermittently throughout each chore to make sure the chain is kept properly tensioned and condition of all parts prior to using. If anything is worn or damaged, replace parts before using them again. A correctly tensioned chain should only pull away from the bar enough to fit a dime between the teeth and the bar. Do not tension a chain after you have finished using the tool. Hot metal expands. If the chain needs tensioning when hot, then allow it to cool, the contracting metal could potentially damage the chain, the bar and even the unit, wait until the next use (or at least until cooled) before tensioning. We have included a video for your reference that may assist you if you experience any challenges. It offers a step-by-step guide to adjusting the chain tension. Please find it here (https://youtu.be/WJOGDpSPzJM).
If you have exhausted all troubleshooting steps and the problem persists, contact us through Live Chat on Greenworks Tools website or call 1-888-909-6757 (1-888-90WORKS). So, our experts can discuss your experience; please have your unit, battery and charger with you along with the model and serial number to complete troubleshooting to ensure quick resolution is provided.