Hello gran1.
Thank you for your question. If the mower stops during use, there could be a few issues that could be causing this.
1) check to see if the unit or battery is too warm. If either is warm the unit may shut off. There is an internal circuit breaker in our batteries. Take the battery indoors and allow it to cool for about 30 minutes and try again.
2) Make sure to start the unit correctly. Always push and hold the safety button first, as the safety button is being held down use your other hand to lift the bale handle. Once the unit starts release the safety switch and continue to hold onto the bale handle.
We ask that you clean out the underdeck of the mower and ensure that the grass bag is empty. Any build-up of debris could affect the performance of the unit and prevent proper power. Do not spray water under the deck of the mower. For caked-on grass, use a scraper to get rid of the grass, and then you can use a damp cloth to wipe off loose pieces. Finish by wiping with the dry cloth. We also suggest removing the blade and fan to clear out any debris around the motor shaft.
If, after attempting the troubleshooting tip and, the problem persists. We recommend contacting our customer support team for assistance with properly submitting a warranty claim. They can be reached either using the online chat function, on Greenworks Tools page, accessible by clicking “Chat with an Expert” in the bottom corner of your screen, Chat with a Live Agent I Monday - Friday: 9:30am – 5pm EST or by calling 1-888-909-6757 between 9AM and 7PM EST, M-F. 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.