Originally Posted by knc1
Most likely, that I2C connection is just the battery temperature sensor.
That is because to "properly" charge Li-Ion, the battery temperature changes have to be monitored to detect "full charge" condition (you can't use terminal voltage detection to reliably re-charge Li-Ion).
Yes, that would make sense. They could even use an I2C temperature sensor! (They're pretty cheap, and much easier to use than an analogue interface.)