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Post: Hello Pavel On the ADC Pi, the A- pins are connected to ground so your voltage measurements will be the input voltage relative to ground. If your battery, DC/DC converter and Raspberry Pi all share a common ground you can use a single resistor to drop the voltage on the ADC input through the built-in voltage divider. You will not damage the I2C bus as the built-in voltage divider combined with the external resistor will drop the voltage to a safe range. The image below shows how you need to connect the 12V battery and 5V wires to the ADC inputs using a resistor on each input. [img]/docs/forumpost/mf79jbi.png[/img] When selecting a resistor for the ADC input you need to use a voltage higher than the expected voltage to allow for a safety margin. A 12V car battery will be higher than 12V when fully charged and can be up to 14.5V when connected to or recently disconnected from a battery charger which is why I suggested a 15V maximum voltage for the ADC input. A 33.2K resistor in series with the 12V battery and the ADC input gives a maximum voltage of 15.059V so you need to multiply the reading from the ADC input by 2.9762 to get the correct voltage. On the 5V wire, I selected a 3.16K resistor which will give a voltage range of 0 to 6V to allow for any drift in the output from the DC/DC converter. Multiplying the ADC reading by 1.1881 will give you the correct voltage.