Why do you think it's the battery if the motor is revving excessively!My 20yr old handheld Dyson died this morning (motor revving excessively) and while it is likely battery I think a new handheld is on the cards. Perfect timing to the OP - thanks
Our hand held Dyson has a Turbo mode which you enable by pressing and holding the centre button on the back of the motor housing. This puts the motor into a much higher speed at the expense of battery life. Pressing and holding the same button returns it to normal mode.