There is something wrong with your setup. With the value shown (100k/10k) on voltage divider you should apply 47.3 V to have 4.3 V on the ADC pin. BTW, your conclusion are right, you can't measure a battery using the same value for reference, even when the battery discharge you'll always reading 1023. Try to use the internal 1.1 V reference, and use an appropriate voltage divider on input.
Ciao, Ale.