Just out of curiosity: how does Apple manage batteries with different sizes?

[rin67630]

The battery of a MBP 2014 15" has 6 cells (2x3 cells with completely different sizes/volume and hence capacity.

The voltage rating is 10.6V which would correspond to 3 cells in series.
But putting different capacity cells in series is a bit silly.
How does Apple manage this dissimetry?
Has someone got a clue?

 

[f54da]

The BMS (battery management system), is responsible for balancing the different cells, for the 2014 Apple just uses an off-the-shelf TI BMS. I forgot the exact part number, but you can look it up. Basically there's nothing apple specific about this.

See e.g. https://www.ti.com/download/trng/do... Cell Balancing - What to Balance and How.pdf

 

[JPack]

Each cell has its own BMS at the bottom of the pouch. If Apple wants to fill the volume of the chassis, they have to put in different capacities.

 

[f54da]

@JPack You probably know better than I do given your extensive supply-chain knowledge, but I thought there was only a single bq20z451 BMS (for the 2014 models)?

See e.g. teardown in https://logi.wiki/index.php/MacBook_OEM,_Aftermarket,_and_Knock-Off_Batteries or https://kaspars.net/blog/macbook-battery-remaining