I believe, the 24V battery is indeed the newer generation from Greenworks designed for cross-compatibility. While the 40V system has been around longer, the 24V system allows for more flexibility - smaller tools can use a single 24V battery, while larger tools like mowers can use two 24V batteries in series (24V+24V) to achieve the same power as the 40V system. This newer approach lets you use the same batteries across more tools in their ecosystem. The 24V system appears to be Greenworks' strategic direction for future product development, making it likely to have longer-term support than the older 40V line.