GSMSIM808 with global sim

Hello everyone i would like to use the forum cause i need some help with my sim808. I am currently using gsm sim808 module connected to arduino. The arduino is powered through usb cable atm and the gsm with 2 18650 li ion 3.7V batteries conected in series so that makes it 7.4V connected to V_in pin. So first question in order to get batter info with AT+CBC command the battery needs to be connected to li-ion pin? cause that pin it only for 3.7-4.2V battery and how can i get the battery info from V_in pin?
Second question is this, i am using a global simcard that supposed to connect to the best signal operator, we have 3 operators in my country and so far it seems that the module is only connected and register to 1 operator and cant connect to the other 2. What i get when its only 1 not working operator is this: +COPS:0,0 and +CREG=0,0. What could be the problem here? SIMcard, operator or something else?
Thank you in advance.