@wslee
I know it's not my business to tell you how to run yours.... I admit I assumed it wouldn't be difficult to implement the car mode until I saw the fw upgrade that brought the "Auto Power Off when Charger Connected" mode - that complicates the logic of choosing a simple car mode or an off while charging mode... they conflict, but I can see a solution by making the 2 options mutually exclusive in the app, a 3 way switch, A, B or neither.
It seems to me that simply polling the state of the charging port for an attached charger that is not a data cable and storing the state of this in the settings storage are the only prerequisites - if I'm wrong, that explains why it's going to be a tricky one.
The other thing I will say is that if the ES100 uses a LiPo battery then discharging the battery fully and then allowing it to just sit that way is not good for the battery (nor is leaving it fully charged for a long period either) it will just degrade the battery a lot faster than cycling it or leaving it at an ideal storage voltage of about 3.85 volts... If killing the battery is the only way to implement a car mode, then it's probably not worth it. I still want the option to use the battery too!
If you find a solution that works, I'd astroturf 100 Amazon reviews for you! (no, just kidding. That's a joke guys... Radsone deserves more respect than that.)
Keep us posted