Crikey Dave, don't encourage him. It could easily get out of hand very quicklyYou could always make a 6S booster pack. You're pretty good at that sort of thing now aren't you? What about a 6S4P pack with a belt clip? Find where the power wires come out of the Dyson's battery and add a change-over switch for the external pack. You'd need a 6S 20A BMS though.