[powerbroker]

Typically, the battery cells that are formed into packs are rigidly arranged. So far as I know, they are arranged to have a common positive cathode by being connected as a single node with a conductor. In other words, they are wired in parallel.

I'm not a chemistry major, but everything I've seen suggests that the parallel arrangement allows them to drain concurrently and maintain a near-identical charge. Now, I'm oversimplifying, because there must be some modest isolation cell-to-cell, that lets these batteries be balanced to get to a near-identical charge level at charge completion.

That said, depleting some batteries, while others remain freshly charged (or adding freshly charged cells) can cause some problems, which I'm sure someone smarter than me will explain. But, for so long as these batteries need to hold a near identical volatage, it is going to be rather challenging to have a partial swap of some of the batteries.

[stop50]

They are connected in a mix. Some cars use 800 V internally,its easier and safer to connect around 200 in a row to get the needed 800 V than to transform it.

[taosimple]

That's right, it's still just a concept, and there are many engineering challenges to overcome.