It makes no difference if it is dead or not. It should take max 3-6 hours to recharge to full power, even if you still have left on the Rechargeable Battery Chargers
There is a big difference in how long it will last. There is a sleep mode when not used most phones take up to 3 days max. But if you use the battery will die much faster. When I go on long trips I have a charger that I can put in the car, so I do not worry about it. I also use the hands free works very well.