Think about it. You are reading the voltage at A5. And it is 2.62V
Your Solar Battery has a voltage of 10.48V.
Your 30k, 10k resistors divide it by 4. Hence you read 2.62V
If you want to see the human-readable voltage:
float voltage = readVal * ((5.0 / 1024) / (10000 / (10000 + 30000)); //scale it to volts
You could calculate the scaling value yourself. If you leave the resistor values in the expression, the Compiler does the maths for you.
The important lesson is: do you understand how to calculate from a potential divider? i.e. resistor values.
And do you understand how to calculate a voltage from the ADC value?
You must write the explanation into your thesis.
The other lesson is: float maths keeps the fractional remainder. integer maths loses the remainder.