Just an FYI to those who seem to not know this bit of info: both the
upper lift gate and
lower tail gate can be opened
manually when there's no electrical power.
And as mentioned above, if you have access to the engine bay and there's no electrical power, you can connect jumper cables or a battery charger or battery pack to the positive & negative jump start terminals in the engine bay...which will provide enough "juice" to actuate the central locking system: