0xAB is device adress ( chip itself ) for read on i2c bus The bq27200 supports the standard I2C read, incremental read, quick read, and one byte write functions. The 7-bit device address (ADDR) is the most significant 7 bits of the hex address and is fixed as 1010101. The 8-bit device address is therefore 0xAA or 0xAB for write or read, respectively