BQ25306: How to connect two single cells (LiPo or LiPO4). Have I to balance it?

Hi everyone.
I need some advice because I'm not very skilled about chargers.

I have two single cells (each with PCM).
I have two possible technologies: either LiPo cells or either LiPO4 cells.

I have to put the cells in series and charge them with a fast charger.

I developed a prototype for the single cell with the BQ25300 and everything works good.

Now, for example, I see the BQ25306 suitable for two cells in series.

How do I balance the two cells? If I have a empty cell and a charged one how does the charger know?

Do I need to select a different charger IC? Should I insert something that balances the cells?

Thank you
Stefano