I once bought a 14 inch Webb battery mower that used a car battery. But the battery only ran for about 5 minutes because it was too old for the job. The reel of rotary blades could not be brought closer to the fixed blade because the adjuster was at the end of its adjustment slot. Why did I buy such rubbish? Simple answer is that I had no money for anything better but I'm and engineer and I knew how to extend the mower's life. Here's what I did. I elongated the adjustment slot which was in cast iron, using a small diameter grindstone. I then replaced the car battery by a mains transformer with a full wave rectifier and a digital voltage controller. I used the battery box as a heatsink for the electronics. After sharpening and adjusting the blades the mower cut perfectly. It lasted about three years with grass trimming twice a week.