this post says that the address is non-programmable on the BQ40Z80:
However the Technical Reference Manual says it can be programmed, in chapter 17 page 102:
"The BQ40Z80 SMBus address (default 0x16) can be changed. The target address should be programmed
in Address and the 2’s complement of that value should be programmed in Address Check.
The BQ40Z80 will check these values upon exit from POR, and if the two data flash values are not valid
or the programmed address is 0x00 or 0xFF, then the device defaults to 0x16."