Yes, there is a manual door lock button-thing on the door next to the door latch. Though honestly I don't know if that works when the power is dead. As cars move to "fly by wire" this becomes a larger concern - less mechanical linkages, more buttons/switches + wires.

For example to open the back you push a button on tailgate and then pull to open. That button is definitely not a mechanical latch, so if the battery is dead then you're not opening the tailgate.

This would be an interesting experience - go to an auto dealer and ask them to disconnect the battery, then see what still functions.