TI clearly doesn't take their own website seriously, since they list the BQ41Z50 as a "drop-in replacement with upgraded functionality" for the BQ40Z80.

Yeah, no.

The Z80 supports 6 series cells while the Z50 supports only 4. So you can "drop-in" the Z50, as long as you "drop-out" two of your series cells. Lies.
https://www.ti.com/product/BQ40Z80