I'm on my sixth year with a sears cordless. It used 2 12v lead acids in series for 24v but they only lasted 2 yrs. I then started using a zippy 6s pack which gives it close to original rpms plus a lot lighter. For normal yard edging it's great but if the grass is a little taller and dense it does get bogged down. Would be nice if they gave output rpms for these cordless trimmers.