With traditional battery banks ie lead acid, as the batteries wore (due to lead sulphation) the voltage would drop. Hence battery meters could measure a battery testing the voltage. But Lithium is different - it maintains its voltage until the battery has almost failed. The capacity of the battery however falls ie how long it can power something, such as providing mileage in a vehicle.
So with Lithium Phosphate Iron batteries (which last longer and are as inflammable as wood) if a cell failed, it would be easy to isolate it, and then replace.
If one has a battery bank that has lost for instance 50% of its expected life, what could one do about that with lead acid batteries? Because the battery bank with lead acid has dropped voltage, adding an auxiliary band of batteries would result in the new batteries doing all the work. So the new batteries would have radically reduced their life, due to trying to increase the dropped voltage of the old batteries, which due to sulphating cannot attain the voltage of a new battery. So the old batteries would absorb the new batteries power and waste their power via heat.
With Lithium it is totally different. Because the voltage stays the same for most of the life of the battery, one can add an auxiliary batteries to the circuit, and hence extend the range of the batteries. Without damaging the life of the batteries new batteries.
But companies do not want that to happen. So each company uses battery managers of their own, and they use voltages that are different from each other company. And then they package the battery packs in unique forms. So at every step, they have stopped customers being able to add "their own fuel". And also, the prices of replacement batteries for cars is outrageous.
The actual cells the companies use, have the same voltages, due to the chemistry of each lithium battery type. So lithium cells could be interchangeable between brands of cars and models of cars. But the car companies did not want that to happen.
Car companies do not want standardised battery banks. Or even interchangeable cells. Also the management of the cells would also prevent non factory battery repairs. And if a car owner replaced a faulty cell in a car's battery bank, the car would void warranties and probably void the owner's insurance policy.
Lithium batteries are quite cheap these days. Typically they cell in 12v and 24 v configurations, and 48v for battery banks for solar, etc. Cars are said to be mostly 400 volts. But some are 800. And the actual voltages vary from even model to model. Electric cars have around 4,000 cells. A 12v Lifo battery has four cells in it. A 12.8 volt lead acid battery has 6 cells in it. Connecting cells in series increases the voltage, while connecting in parallel keeps the voltage the same and increases the capacity or mileage. So a car make can add up the same cell outputs, to produce a battery bank that has a different voltage to another car the maker sells. An example is the varying voltages from one Tesla model to another.
The companies looked at how tough the battery business is, and hence decided to prevent competition. And probably electric vehicles could be very long life. Low maintenance too. But for the batteries. No wonder car owners see a standardised battery as killing future sales.
Politicians don't care about the best way - they just chase votes IMO.
I have a sailing yacht, it has batteries, so I'm aware of many of the issues.