Originally Posted by
Mitsu3000gt
I have a similar yard to you, not much grass in the back yard but maybe a bit more grass with the front yard. I'd go at least 40V, the 18V kits have such little power if your lawn ever gets really long or a bit wet they tend to struggle. That being said the 18V kits have so many other tool options, since all the hand tools take the same batteries. For non-professional 18V I'd still go Ryobi, the sheer amount of choices for their "One" series hand tools is ridiculous, so if you ever need anything in the future you can just grab the cheap bare tool. Warranty is 5 years, they are very cheap, surprisingly well made for the price, and you have 90 days to return them to Home Depot if needed. Otherwise I would go at least 40V so you get more power for your mower/trimmer/edger. I was going to buy an EGO until I saw how big they were, and you need to spend around $800 just to get a brushless motor - they make good stuff, just overkill for small yards.
As for the difference, with 40V system you are getting a lot more power and longer run times, but fewer overall tool choices should you want to expand (most of the 40v tools are yard-care related, whereas the 18v system covers pretty much everything).