You could test by using a potentiometer such as this… just make sure not to exceed the voltage… maybe add a led inline… set the potentiometer to 0 and connect to the 8.5v then start running the analogue to digital sketch… then slowly turn the pot till the reading max out at 1023… then STOP!.. do not turn it any higher you will burn out the pin… then measure the resistance of the pot
You might could use a setup such as this
also you need to common the ground