I have one. They come in different sizes, with different width blades and
different size batteries. Mine's a smaller one, but it claims to be able to
mow 1/3 of an acre (4000 m^2?) on a charge. My yard isn't anywhere near
that big, so I find that I am more limited by leakage. Even so, I can mow
for a couple of weeks on a charge. (Actually, my yard is mostly dead anyway,
so in those couple of weeks I'm likely to mow only a few hundred m^2.)
The mower is pretty heavy, but not much more than a gas engine would be.
It's Wonderfully quiet -- it sounds like a largish fan.
I'll be bowing out of the mailing list. You have lots of neat ideas, but
the traffic is more than I can keep up with. I would love to hear from
you when you have a design worked out.
Chris Kingsley