I have Ego's bicycle handle brush cutter, think a weed whacker on steroids with a metal blade.

That think does some serious work. I've cleared acres of overgrown mess with it. 2 6aH batteries will outlast me (~2 hours) before I need a break and the fast charger tops one up in maybe 30 minutes.

Lawn mowers are really where batteries fall apart. They go through a charge extremely fast, especially if the grass is even moderately overgrown. Most mowers are meant to be finish mowers where you aren't taking off much grass at all, say 1/4" up to maybe 1". Electric mowers really demand that or you'll run out of juice very fast.