Really don't understand that. a normal extension lead can carry the current that it is designed for, being a u.k. standard of 13A at 250 volts. as long as the extension cable is not on a reel it will be fine. if its on a reel, and you only reel out enough to reach the plug, and therefore leave a coil on the reel, it will produce heat, and melt the insulation, short out and fuse or start a fire. some vacuum cleaners have rewind devices, and if you only pull out enough cable to reach around the room, the length left inside the rewind will get seriously hot and melt. So, I would say that using an extension lead will have no effect on the recharge, as voltage loss due to cable resistance over a few metrs will be almost nil.