I got a free laptop that has a stuffed battery so I thought I would tear it down.
The BQ9000 is a custom gas gauge ic with no public datasheet. It may have signature validation of the eeprom to stop 3rd parties making compatible batteries.
The shunt resistor is small, so the losses must be low meaning the resistance must also be low.
The thermal fuse over the MOSFETs
Back to back MOSFETs