Firstly, apologies if this post overlaps with other similar recent threads.  I've read through but haven't really got the kind of info I was looking for.

I need a lawn mower (getting annoying having to borrow the lawnmower from my ex every few weeks or so, especially with summer arriving).  The previous lawnmower was a pretty decent Masport President 140cc petrol mower with a steel chassis.  A similar model costs between $450 and $570 locally.  But as I'm looking at getting into battery powertools with a consistent ecosystem, I'm wondering about a cordless mower as well.  My total lawn area is less than 350sqm, all mostly flat.

I understand that for a tool like a lawnmower, a higher voltage rating is better (say 40v or higher). Ryobi have some models that are 18v or 36v, but are these 36v tools using a single 36v battery (which I assume isn't compatible with the 18v tool range), or are they using 2x18v batteries? For the area I'm mowing, how essential would the higher voltage models be?

Most of the cordless lawnmowers are polymer decks, as opposed to steel.  I understand that steel units are heavier, so drain the battery faster, but would be more resilient to cracks and breaking.  Is the steel deck worth it?

From a long-term maintenance perspective, how does a cordless mower stack up against a petrol one?  If you assume one service per year (I think the last one was about $120) plus petrol, then the annual running costs would be less than $200/year.  For a cordless mower, presumably the only service costs are to sharpen the blade, and electricity costs (not sure what they would add up to, but I guess it would be less than petrol).  Over a 5-year period I suspect the cordless option works out better, but I'm guessing they probably wouldn't last as long as a well-maintained petrol mower (up to 20 years).  Anyone crunched the numbers on this side of things?