To replace the battery - open the case, prying the gap between the halves with a fingernail or a plastic card (do not use metal objects). Remove the old battery by pushing it from the inside with a narrow plastic object. Install the new CR-2032 battery with the narrow side (negative contact) to the board. Hideez Key-2 will beep and then ready to go.
All user data is stored in non-volatile memory, when power is turned off (removing the battery), it is stored.