Update mkr-battery-app-note.md

Fix data type of variable max_Source_voltage. Float is correct here to get correct values.
Made calculation of the two voltages better. No real change, but more accurate results this way.

Author: fl43

content/hardware/01.mkr/01.boards/mkr-wifi-1010/tutorials/mkr-battery-app-note/mkr-battery-app-note.md

@@ -124,7 +124,7 @@ We will go through the lines needed to create a Sketch to read the battery value
 **4.** We will now create a variable to store the maximum source voltage `max_Source_voltage` as well as the upper (`batteryFullVoltage`) and lower (`batteryEmptyVoltage`) values for the battery. We will also define the battery capacity as `batteryCapacity` so as to determine the charging current. Since we are using a 750 mAh battery in this example, we will set the value to `0.750`.
 
 ```arduino
-  int max_Source_voltage;
+  float max_Source_voltage;
 
   float batteryFullVoltage = 4.2;
   float batteryEmptyVoltage = 3.3;
@@ -303,8 +303,8 @@ void loop()
 {
   
   rawADC = analogRead(ADC_BATTERY);                     //the value obtained directly at the PB09 input pin
-  voltADC = rawADC * (3.3/4095.0);                      //convert ADC value to the voltage read at the pin
-  voltBat = voltADC * (max_Source_voltage/3.3);         //we cannot use map since it requires int inputs/outputs
+  voltADC = rawADC * 3.3 / 4096.0;                      //convert ADC value to the voltage read at the pin
+  voltBat = max_Source_voltage * rawADC / 4096.0;       //we cannot use map since it requires int inputs/outputs
   
   int new_batt = (voltBat - batteryEmptyVoltage) * (100) / (batteryFullVoltage - batteryEmptyVoltage);    //custom float friendly map function