Do different tools come with different battery runtimes even if they are the same voltage?

Yes, batteries of the same voltage do not necessarily have the same amp hour rating, so the run time will vary based on the battery.

For example, BLACK+DECKER's 18 volt line of lawn and garden tools (string trimmers) use higher capacity (Amp Hours) 18 volt batteries than BLACK+DECKER power tools (cordless drills). Even though the 18v outdoor tool battery and the 18v power tool battery are interchangeable and will work in either tool, the performance of each of these tools is dependent on the capacity of the battery. Therefore, if you own both 18 volt outdoor tools and 18v power tools, it's a good idea to mark which batteries came with each tool to ensure that you are optimizing your runtime and performance.