I have built a battery level indicator and have tested with a 12V battery Would it harm my arduino board if I connect a 48V battery? - Arduino Stack Exchange
12v Battery Efficiency Monitoring using Arduino and Cell App with Database - YouTube
Digital voltmeter to monitor two boat batteries - Project Guidance - Arduino Forum
Measuring 12v battery voltage - General Electronics - Arduino Forum
Monitoring batteries voltages connected in series combination using arduino uno and utilizing relay technique