Battery voltage isolated monitoring on Microcontroller
That size of battery could provide several tens of amps to whatever load it connects to. This means that hanging a simple ADC and voltage divider off it may incur significant errors if the ground return current is high. It could even damage the ADC if not done with due care and attention.

I'd be tempted to "isolate" the ADC with a differential amplifier. The differential amplifier produces an output that can be ground referenced to the ADC circuit rather than ground referenced to the negative leg of the battery: -



Battery would connect across V1 and V2. Use high value resistors to prevent significant discharge current over a long time period depleting the battery. R1 and R2 can be in the several Mohm range.