Paul1977:
I've read about the 2x 18V models, but I can't see anywhere in NZ that sells them unfortunately. Which is a shame because it would definitely be the way to go.
Yeah, I'm 99% sure that Ryobi is exclusive to Bunnings, so you won't find their mowers anywhere else - and it looks like they don't sell the 2x18v model any more. It was still around when I purchased a 1x36v mower from them about a year ago, but I can't find it on Ryobi's website now: https://www.ryobi.co.nz/outdoor/products/list/category/lawn-mowers
Edit: meant to add - be very sure BEFORE you purchase it that you can return the 18v model if it's not adequate for your purposes (and I'd be surprised if they do this), as it's surely false economy if you end up having to purchase a second mower if the first proves to be inadequate for the job (especially, given the experience of others).
That's why I'd recommend seeing if you can borrow a mower before you purchase. Personally, I'd suggest it's worth saving a bit more money and buying a 36v model (given the 2 x 16v doesn't seem to be available). I don't have any of the problems with my 36v that Dynamic's having with the 18v model