Basically I will be receiving the device just before I goto work for a 8 hour shift. I've read a few threads that say two different things, "run down the battery life that comes with the handset," and "charge the device turned off for x amount of hours.". I've always gone with the second one personally, but if I was going to do that would it be safe to leave it on charge for between 8-9 hours? Any help/advice would be much appreciated. Many thanks.