battery V/A reading

does any one knows how to check a batterys voltage with arduino (if possible amps too) but the problem is the battery is 12.6V and 4A.....so there is any way???? maybe the AREF pin????

Use a voltage divider to lower the voltage so the maximum is less than 5. Input that to one of the Analog input pins (not the AREF).

You can try a 3.3K and 10K resistors wired like this:

12V ------ 10K ------ Analog in ------- 3.3k ------- GRND

You can calculate your voltage like this: voltage = (analog in) * 5/1024 * (10+3.3) / 3.3 or voltage = (analog in) * 0.01966

Don't forget to use floats when you have decimals.