The device uses I²C compatible interface for flexible parameter programming and instantaneous device status reporting. I²C is a bi-directional 2-wire serial interface. Only two open-drain bus lines are required: a serial data line (SDA), and a serial clock line (SCL). Devices can be considered as controllers or targets when performing data transfers. A controller is a device which initiates a data transfer on the bus and generates the clock signals to permit that transfer. At that time, any device addressed is considered a target.

The device operates as a target device with address 0x6B (0x4B for BQ25858B-Q1), receiving control inputs from the controller device like a micro-controller or digital signal processor through the registers defined in the Register Map. Registers read outside those defined in the map, return 0xFF. The I²C interface supports standard mode (up to 100kbits/s), fast mode (up to 400kbits/s), and fast mode plus (up to 1 Mbit/s). When the bus is free, both lines are HIGH. The SDA and SCL pins are open drain and must be connected to the positive supply voltage via a current source or pull-up resistor.