I've had an Ego push mower for a few years. I'm now back on enough property that my riding mower is used more, but the lightweight, always ready push mower is nice for hitting the little spots, and for the long "hillock" that the riding mower can't quite traverse safely.
What really showed me the difference between old and new battery powered lawn tools was the leaf blower. My old 18v B&D was only good for running the batteries down before recharging (something that is of questionable value anyway). I could turn it on and run down a battery in two minutes or less. The EGO 56v lasts for awhile, and actually has plenty of power, too. So I've got the push mower, string trimmer, blower, and chainsaw. Still looking to get the hedge trimmer - I got most of mine used or as bare tools, and found deals here and there on batteries.
I was given a B&D string trimmer and hedge trimmer, they both run off 40v batteries. They're good, but I think the tools running 56, 60 or more volts are the way to go. I also get the impression that many of the newer tools are designed a bit better.
(edited to add)
I have 3 batteries, so if I know I might run all three down, I throw the first one on the charger and it is usually charged again when #3 dies. That's with the yard tools, so it's time walking around and cleaning up also. It's very rare that I run all 3 down, and the 1st one again. With the mower, if I was to try and mow a good sized lawn, I'd probably run the third one down and also run the first one back down again if I was mowing constantly. They do make a fast charger that takes, maybe 15 minutes? Not sure. They also make higher capacity batteries, but I don't have any of those - I probably wouldn't need more than two batteries total. Again, because of the deals I was finding when I got into this, I think all but one are the lowest capacity batteries.
Handy thing about the model of mower I have is that you can stick a battery on top of the mower deck, sort of tucked into a built-in handle, and have it right there to swap out.