Can I "Stack" 2-Cell Li-ion Battery Balancers for a 4-Cell battery?

Question

I'm building a project where I need an internal rechargeable battery. I've decided to go with 4x 18650 Li-ion cells, so I can change them if necessary, the 4x 18650'ies will be used in series, for a higher voltage range.

As the cells are in series, I need balancing, but have had some issues finding one I've felt comfortable using, but have been looking at TI's "BQ29209" voltage protection chip, as it comes with automatic cell balancing, however it is made for 2-cell batteries.

Thus the question: would I be able to "stack" two of these, to provide cell balancing for my 4-cell "pack"?

What I'm initially thinking might work would be connecting them like so;

The circuit is adapted from the datasheet for the BQ29209, referencing the Typical Application circuit for a 2-Series Cell Configuration found on Page 13 of the Datasheet, seen here:

Product Page Datasheet

From what I can tell, the BQ29209 only 'needs' the connections to the negative terminal of cell 1 and positive terminal of cell 2 in order to power itself and provide balancing, but I could use a second opinion.

Answer 1

You should not stack battery balancers like this.

In this configuration Cell 3 and 4 are balanced separately from Cell 1 and 2. You could easily have a mismatch between Cell 3 and 1 and your circuit would not prevent this.

If you want to have 4 LI-ION batteries, look for balancers which support at least 4 cells.