I had Ryobi 18V weed whacker, it just wasn't enough power for clumps of grass that only got trimmed 3 or 4 times a year! So I got the 40V Ryobi trimmer. It has plenty of oomph! When I sold the farm, I sold the 40V to a neighbor for 50% of what I paid for it the year before, he jumped on it very quickly! The 18V I gave to my Son-In-Law, he mows six rental properties and has 2 good gas powered trimmers, but when the 8 year old grandsons are helping, the boys are safe, yet the is enough oomph for regularly trimmed grass!
Ivan