Unlock the door with your key.
NO! where does the power (voltage and current) come from if the battery is flat/dead?
If the battery goes dead flat the door will still unlock manually with the key.
Use another vehicle to jump start it, or replace the battery, or charge the dead battery with a charger.
The battery is dead, you are going nowhere so why take the handbrake off. But, if you insist, just connect a good battery to the dead battery and jump start the engine.
A car with a flat (dead) battery usually sounds dead - as in no sound. If you turn the key, trying to turn the engine on, chances are it will make no sound at all, or may make a sort of 'clicking' sound, or possibly a faint intermittent sound.
You may have a flat battery or a bad connection at the battery terminals.
either the alternator is dischargeing the battery or it is going flat just because its not getting re charged
How to unlock vu with flat battery
there wont be any electriity once it is flat!!
Yes, but you will have to connect the jumper cables and let the donor car run for about 15 minutes to get enough charge in the dead battery so it will start the car.
All it is is flat, dry, and dead
If your battery is dead then you are going nowhere therefore why would you need to take the car out of park? Get a jump start from another car with a good battery and then you can start your car and drive to the nearest battery dealer and buy a new battery if need be. Otherwise just put a battery charger on your battery and let it fully charge.