Run-time is tricky
Run-time, which is how long a tool can run before the battery dies, is almost impossible to determine under real-world conditions. It depends on how hard the saw is working. That said, there are two battery ratings that can help: amp-hours and watt-hours. Basically, they tell you how much power a battery can store. We give the watt-hour ratings on p. 52. We used batteries with the highest ratings available. They’re larger, heavier and more expensive than other batteries that fit the same tool.