My 20v 1/2" DeWalt XR impact wrench is rapidly approaching 10 years old. I still have the original 3 and 4ah batteries it came with, they still work great almost 10 years later. I have a 20V DeWalt XR - 1/4" driver, 1/2" drill, 4.5" grinder, sawzall, palm sander, LED droplight, leaf blower, string trimmer, 12" chainsaw, 8" pole saw, and hedge clippers. All work beautifully. I can use a couple of 5ah batteries and weed wack most of my 1 acre property.
I did get their 20" 60v chainsaw, which is a "flex volt" so I can use the 60v batteries for it in my 20v tools as well. The 60v batteries end up being 12ah 20v's, so, they power my yard tools longer than I'd ever want to use them in one stretch. My only complaint with the 20" 60v saw is it comes with a larger motor than the 16" and 18" bar versions of that saw, and if you really put the 20" bar version of the saw to work by cutting 18" and 20" rounds the motor discharges the batteries fast enough that they hit their heat limit. Not that the charge runs down too fast, but they discharge too fast and heat up. Basically the motor on that saw can pull too much for that style of battery/the heat protections it's programmed with. But the only times I've had issue with that is bucking up 18"-20" diameter trees, so, making multiple, back to back full bar length cuts. Even still, with a couple of 12ah batteries you can cycle them and basically get a tanks worth of cutting done compared to a gas saw. Not what you'd want to do a days worth of saw work by any means, but to have as a back up in case a tree goes down across the road in the winter it's awesome. If you do a lot of cutting for the price of the 20" 60v saw you're probably better off with a regular gas powered chainsaw to run a 20"-24" bar. But for bigger "homeowner" type stuff the 60v saw is pretty handy. And the fuel never goes bad, the carb doesn't gum up, no need to have mix fuel sitting around, etc.
Of all of them the 20" chainsaw is the only one I'd ever buy a gas powered version of. I haven't used an air impact in years, and I've got a couple of nice ones. Same for corded tools, just no need for them at all with the 20v DeWalt stuff.