+-----o Vbatt
                  |
               R1 #     -
                  #       } Vr1
                  |     +
                  +---------o Vmeas
                  |
               R2 #       +-
                  #       |
                  |      ---
         Vlcd o---+      GND

 
 ADC_LCD_V_MEAS = ADC_VBATT + ADC_LCD_V_R1
 ADC_LCD_V_R1 = (ADC_LCD_V_LCD - ADC_VBATT) * (ADC_LCD_R1 / (ADC_LCD_R1 + ADC_LCD_R2))
 =>
 (ADC_LCD_R1 + ADC_LCD_R2) * (ADC_LCD_V_MEAS - ADC_VBATT) = ADC_LCD_R1 * (ADC_LCD_V_LCD - ADC_VREF)
 =>
 ADC_LCD_V_LCD = ((ADC_LCD_R1 + ADC_LCD_R2) * (ADC_LCD_V_MEAS - ADC_VBATT)) / ADC_LCD_R1 + ADC_VBATT

---