Hello bmp769.
Thank you for your feedback. We are glad to hear the replacement 24V 4.0Ah batteries are compatible and that the mower is now running, but we understand your concern about the runtime. Runtime can vary based on grass conditions, cutting height, and the load on the mower. Thicker or taller grass and lower cutting heights require more power and can reduce overall run time. For best results, we recommend mowing regularly, avoiding cutting more than one-third of the grass height at a time, and making sure both batteries are fully charged before use. If you feel the runtime is still not meeting your needs, please continue working with our success team so we can review your setup and discuss the best next step. They can be reached either using the online chat function, on Greenworks Tools page, or by calling 1-888-909-6757. Depending on your mowing needs, adding an additional battery or upgrading to a higher-capacity battery may help extend run time and improve overall performance. They can be reached either using the online chat function, on Greenworks Tools page, or by calling 1-888-909-6757. We appreciate the opportunity to help and want to make sure you have the best possible experience with your mower.