@surfer63 @abidali I have tested and dudu shows voltage in the status bar measured from its own power supplied. When obd dongle is connected this changes to a value from obd.
Putting aside accuracy of Dudu's own voltage measurement, voltage at Dudu power socket usually always will be lower than obd, as usually wires connecting a radio to battery come not very thick and loses are unavoidable. That's one thing. Second thing is obd dongles do not measure voltage at the battery but voltage at the obd socket, as OBD protocols for car battery voltage vary very much so that would not be feasible. And again, voltage on obd socket is higher than at the radio as usually it goes shorter route to the battery.
As for battery voltage in my case it can be taken via obd service mode from canbus enabled fuse box next to the battery but to be honest implementation of it would be again not feasible for every car.
So, my obd dongle shows 13.8V with engine running, canbus shows 14.4V which is consistent with what i saw always, obd voltage is usually half a volt lower than nominal at the battery.
Brings me to conclusion, if you see 15 volt on obd, you're frying your acid battery as the charging voltage might be around 15.5V.
And of course voltage will be fluctuating depending on engine load and your alternator state.
