and some other hardware, like motor
But how can I read with the same precision also when motors will be on?
I have yet to see an accurate measure of battery life in a varying load environment, just look how accurate the average lap top is.
The best we can do is to select some minimum battery voltage below which is not safe for the battery or not reliable for system operation. Then we can monitor the battery voltage and shut down the system at this pre-determined minimum voltage.