Primary / Secondary
The aluminium in the battery gets consumed in the process, that is why it is a better bet to have the aluminium battery act as the secondary energy source in your car. The primary battery will be for example a lithium based one that is sized for your normal daily usage. In the West, average daily usage of a car is 39km a day. In this way, the size of the lithium battery can be decreased from the 'standard' 150km to be suitable for just 50km. This is enough for the average trip you would make, decrease the lithium battery to a third of its original size and result in a lighter/cheaper solution. The aluminium battery gets added and gets used only when you have to drive a longer trip.
The lithium battery provides the power for your basic mobility and if you need more, you can 'borrow' the extra energy from the aluminium battery. It is similar to the credit line you have with a bank. The aluminium battery is a credit line for energy which you can draw from when you drive a longer trip.