Depends on how they are connected. If you just stack the second set on top of the first you will have a serial connection, making a 4S2P setup, which means the voltage will double but the capacity will remain the same. If the two sets are connected side by side you are basically making a 2S4P setup, where the voltage remains the same but the capacity doubles.
Since in most cases a driver is not designed to handle a doubled input voltage, connecting the two battery cages in parallel would be the way to go. That would make for some interesting design challenges in creating the appropriate container.