Calculating battery percentage using an Arduino
I think your calculation is OK.

Proof:

If your ADC conversion results is 1024 (full scale 10 bit) - when AVcc = reference

result = 1126400L / 1024 = 1100;


If your ADC conversion results is 512 (half scale 10 bit) - when AVcc = reference / 2

result = 1126400L / 512 = 2200;


Your percent result is -4% because voltage is below 3V.

percent = ((volt-3)/0.7)*100
-4 = ((volt-3)/0.7)*100
-4/100 = (volt-3)/0.7
-0.04*0.7 = volt - 3
-0.28 + 3 = volt
 2.972 = volt