I work on small engines on the side, and battery powered stuff definitely has its place. I recommend them to a lot of my customers who use small hand held equipment sparingly, because they are easier to manage and less of a hassle. A battery powered fleet is great for someone with a small yard as well. Quieter, no dealing with fuel issues, oil changes, mixing fuel, exhaust, etc.
Those Ryobi mowers a few posts up seem like an interesting idea, but I'm not surprised they don't sell well. Ryobi and Cub Cadet aren't really known for quality, especially since Cub Cadet has been putting out MTD re-branded mowers at Lowes for several years now. Their quality has been improving, but I know many people who won't touch them anymore. Ryobi is one step above whatever store branded tools the box store carries. The electric zero turns have a niche market currently, because most people who run zero turn mowers have a lot of mowing to do. It isn't the power provided by the electrics, it's the charging. If it has to charge for 4 hours every time you mow 2 acres (assuming the efficiency is perfect) then you will not be mowing a lot of lawns between charging. Most people in my area have at least a 2 acre lawn. It might work for a homeowner, but not for someone mowing more than 1 lawn, and that's leaving the higher purchase price out of the equation.
I watched a video about a guy who ran a mowing service with an electric zero turn. They made it work but he had a massive trailer outfitted for charging several batteries, which cost quite a bit, and solar charging was involved as well to even make it feasible.
Like I said I admire the innovation, but they have the same infrastructure and charging issues for heavy users as EVs do, it's just hard to compete with the ability to re-fuel instantly with gas stations on every corner.