It seems that, to use I2C, we need to:
un-blacklist I2C with
sudo nano /etc/modprobe.d/raspi-blacklist.conf
enable I2C kernel module with
sudo nano /etc/modules
Why is it disabled + blacklisted by default? This sounds like a high-level protection against I2C!
If I enable it, will it cause higher power consumption?
This question is important because my RPi will be battery powered.
(I can avoid I2C and use SPI instead if it is better for power consumption).