
I'm still working on cutting up that large tree that I felled the other day. Yesterday, when I was out there bucking up the tree trunk, my 4.0 Ah battery went dead in a very short time - like maybe only 10 minutes.

I put the battery on the charger, but it was too hot to charge. When the battery cooled down, I notice that there were still 2 bars, out of 4, on the battery. So, what I learned is that the battery overheated and shut itself down to protect itself.
With that knowledge in mind, today I would cut a bit with one battery, and then swap out the other battery for a few more cuts. In that way, I was able to fully drain both batteries before they overheated, and I suspect I got maybe 50% more work out of them by swapping them out every few minutes.

By the time both batteries were dead, they were truly drained all the way down and not just shut off due to overheating. Live and learn.
Another advantage to swapping out the batteries to prevent an overheating shut down, is that the batteries will take less time to cool down before the chargers will start recharging the batteries.
Normally, I'm only trimming up branches that fall to the ground after a windstorm. My little 40v chainsaw can do that a very long time and not overheat. The batteries stay relatively cool when stopping and starting all the time when trimming. However, cutting up a 20 inch trunk, with constant running and no stopping, will overheat the batteries pretty fast. Obviously, a 14 inch 40v chainsaw is probably not the best choice for cutting up a 20 inch tree trunk, but I wanted to see how it would perform on that job and I have been learning how better to use my 40v batteries and chainsaw on a bigger job.