BQ25120A: i can not access i2c in battery only using.

I am developing a product(wearable band)) using BQ25120A.

I set the CD pin low at initialization.
I can access i2c if USB is connected.
I can read the state of the Ship contrl register.
Charge in Progress, Charge Done, and so on.

However, I can not access i2c when using Battery only.

To access i2c in battery mode, it is only possible after making the CD High.
However, if CD is High, Charge Status (Charge Done, Charge in Progress) of Ship control register does not appear. Why?

And how do I check if I have a USB connection?
VINDPM_ON is always 1.

Thank you.