At the end, I opened 3 button card without damage IC inside.
It was too difficult, but succeed
It has one rechargeable battery inside, Panasonic VL 2020.
One of the terminal was broken; I soldered it.
But I'm afraid that battery was discharged.
I traveled 70km, replace standard battery (CR 1620) with new one, but still handsfree not working.
Does anybody know how to charge it?