I also wrote a simple program: See retu-adc.c (or retu-adc for the binary) here:http://my.arava.co.il/~matan/770/

Run retu-adc to read all ADCs, or retu-adc 8 9 to read the battery voltage only.

To get a reasonable battery level, you need to take into account the temperature, charging status, and current draw, if it is also available somehow.