The [Ego] chainsaw is quite capable, but it's a relatively small saw (16" blade). Perfect for most backyard type applications, and it handily cut through a 5" pressure treated fencepost that I was replacing and had to cut to length.

The real issue with bigger trees would be the blade length, not the battery (well, unless you're taking an entire tree down in which case you'd need extra batteries).

Also, like any chainsaw, keeping the blade sharp is also key.

No, I haven't had to take any trees down, this is mostly for trimming and chopping up fallen branches etc.