Sim808 + Arduino Pro mini + 2 battery by 3.7 = not work

Good afternoon, everybody.
I collecting scheme sim808 + Arduino Pro mini (pictures attached), the purpose of providing a GPS and further sending to the server. All put together, wrote, connected to USB - all is ok - data is send to server (AT CGNSINF CGNSINF: 1,0,19800106004030.000 , 0.00,0.0,0 , 0,0 ,), the quality of determination not happy (very long send zeros).
I whant to test GPS outside, for it I needs autonomy.

I connected 2 battery by 3.7V = 7.4V, (in datasheet wrote that arduino + sim808 must work on 3,7, but it did not network diode not blink.
Connected battery to Adruino, all is make up (Arduino and Sim808) but it send the void, that is, the diode flashes (sending data), the data arrive on a server at a rate of one byte - space, if I connect to the USB - all the rules.

Can someone tell me what could be the problem? … Thanks in advance for any hint! Attached is the code:

#include <SoftwareSerial.h>
#include<stdio.h>
#include<string.h>
#define DEBUG true


SoftwareSerial mySerial(7,8); 
        
void setup()
{
  Serial.begin(9600);
 mySerial.begin(9600); 

 
        
}
String Serialread;
void loop()
{

StartGPRS ();
String GetData;
mySerial.println("AT+CGNSPWR=1");
GetData = mySerial.readString();
mySerial.println("AT+CGNSSEQ=RMC");
GetData = mySerial.readString();
mySerial.println("AT+CGNSINF");
GetData = mySerial.readString();
        delay(1000);

  GetData.replace("\n", "");
  GetData.replace("\r", "");
  GetData.replace(" ", "");
Serial.println(GetData);
SendData (GetData);

CloseGPRS ();


delay (10000);

}

void StartGPRS (void)
{

mySerial.println("AT+CMGF=1");
Serial.println(mySerial.readString());
mySerial.println("AT+CGATT=1");
Serial.println(mySerial.readString());
mySerial.println("AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"");
Serial.println(mySerial.readString());
mySerial.println("AT+SAPBR=3,1,\"APN\",\"internet\"");
Serial.println(mySerial.readString());
mySerial.println("AT+SAPBR=1,1");
Serial.println(mySerial.readString());
  
}

void SendData (String DataForUrl)
{


  
mySerial.println("AT+HTTPINIT");
Serial.println(mySerial.readString());
mySerial.println("AT+HTTPPARA=\"CID\",1");
Serial.println(mySerial.readString());


mySerial.println("AT+HTTPPARA=\"URL\",\"<a href="/sim808/index.php?gps_data=">http://*******/sim808/index.php?gps_data=</a>"+DataForUrl+"\"");
Serial.println(mySerial.readString());
delay (3000);

mySerial.println("AT+HTTPACTION=0");
Serial.println(mySerial.readString());
mySerial.println("AT+HTTPREAD");
Serial.println(mySerial.readString());
}

void CloseGPRS (void)
{
mySerial.println("AT+HTTPTERM");
Serial.println(mySerial.readString());
mySerial.println("AT+SAPBR=0,1");
Serial.println(mySerial.readString());
}

sim808.jpg