Measuring motor's battery level

Using Arduino General Electronics
1

I have and ESC with brushless motor connected to Arduino. It uses separate 12V battery as a power source, while Arduino uses USB from my PC for now. I want to measure voltage of battery in order to check its battery level. For this, I have one wire connected to + and - battery's wires through resistors, and to analog pin on arduino (I want to read voltage from this pin). My question is - what kind of resistors do I need in order to prevent Arduino from frying?

Schematic attached.

Thanks in advance.

BatteryLevel1.jpg
BatteryLevel1.jpg933×604 31.2 KB

2

I use a 100K and a 25K 1/4Watt gives a voltage of 5V for an input of 25V. If the voltage is higher there are voltage dividers on the web to calculate for an output of 5V max for you

3

I'm using:

12v----15k---+---8.2k----GND
|
A0
4.24V, (4.95v @ 14V supply) R2 / (R1+R2) = 0.353448275862