I have a pair of battery Dysons as well, both V8's. Despite my initial reservations before getting them, I have to say they do work for day to day vacuuming. Given the amount of dust we get here, I have a vacuum out round some part of the house daily.
But we still have the corded vacuums for those days when you move the furniture and clean properly.
The batteries on the V8 are "almost good enough", and last about 20 mins on normal setting with a motorised brush bar. Or about 15m on max mode with a crevice tool. Which is usually good enough to do a quick vacuum of entire house, or vac the car.
The battery inevitably fails after 3 or 4 years (not bad, seeing ours live on their charging docks), but there are plenty of chinky replacements for £25, and they are easy to change, like most Dyson parts.